diff --git a/shrooms-vb-core b/shrooms-vb-core
index ae22c95..b4b9131 160000
--- a/shrooms-vb-core
+++ b/shrooms-vb-core
@@ -1 +1 @@
-Subproject commit ae22c95dbee3d0b338168bfdf98143e6eddc6c70
+Subproject commit b4b9131f3976388b096343725fce1bdf35f4e3df
diff --git a/src/app.rs b/src/app.rs
index a5d62ac..91b9381 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -5,6 +5,7 @@ use std::{
 };
 
 use game::GameWindow;
+use input::InputWindow;
 use winit::{
     application::ApplicationHandler,
     event::{Event, WindowEvent},
@@ -14,7 +15,7 @@ use winit::{
 
 use crate::{
     controller::ControllerState,
-    emulator::{EmulatorClient, EmulatorCommand},
+    emulator::{EmulatorClient, EmulatorCommand, SimId},
     input::InputMapper,
 };
 
@@ -28,6 +29,7 @@ pub struct App {
     input_mapper: Arc<RwLock<InputMapper>>,
     controller: ControllerState,
     proxy: EventLoopProxy<UserEvent>,
+    player_2_window: Option<WindowId>,
 }
 
 impl App {
@@ -40,19 +42,19 @@ impl App {
             input_mapper,
             controller,
             proxy,
+            player_2_window: None,
         }
     }
 }
 
 impl ApplicationHandler<UserEvent> for App {
     fn resumed(&mut self, event_loop: &ActiveEventLoop) {
-        let mut window = GameWindow::new(
+        let window = GameWindow::new(
             event_loop,
+            SimId::Player1,
             self.client.clone(),
-            self.input_mapper.clone(),
             self.proxy.clone(),
         );
-        window.init();
         self.windows.insert(window.id(), Box::new(window));
     }
 
@@ -63,9 +65,9 @@ impl ApplicationHandler<UserEvent> for App {
         event: WindowEvent,
     ) {
         if let WindowEvent::KeyboardInput { event, .. } = &event {
-            if self.controller.key_event(event) {
+            if let Some((sim_id, pressed)) = self.controller.key_event(event) {
                 self.client
-                    .send_command(EmulatorCommand::SetKeys(self.controller.pressed()));
+                    .send_command(EmulatorCommand::SetKeys(sim_id, pressed));
             }
         }
         let Some(window) = self.windows.get_mut(&window_id) else {
@@ -74,13 +76,30 @@ impl ApplicationHandler<UserEvent> for App {
         window.handle_event(event_loop, &Event::WindowEvent { window_id, event });
     }
 
-    fn user_event(&mut self, _event_loop: &ActiveEventLoop, event: UserEvent) {
+    fn user_event(&mut self, event_loop: &ActiveEventLoop, event: UserEvent) {
         match event {
-            UserEvent::OpenWindow(mut window) => {
-                window.init();
-                self.windows.insert(window.id(), window);
+            UserEvent::OpenInputWindow => {
+                let window =
+                    InputWindow::new(event_loop, self.input_mapper.clone(), self.proxy.clone());
+                self.windows.insert(window.id(), Box::new(window));
             }
-            UserEvent::CloseWindow(window_id) => {
+            UserEvent::OpenPlayer2Window => {
+                if self.player_2_window.is_some() {
+                    return;
+                }
+                let window = GameWindow::new(
+                    event_loop,
+                    SimId::Player2,
+                    self.client.clone(),
+                    self.proxy.clone(),
+                );
+                self.player_2_window = Some(window.id());
+                self.windows.insert(window.id(), Box::new(window));
+            }
+            UserEvent::Close(window_id) => {
+                if self.player_2_window == Some(window_id) {
+                    self.player_2_window.take();
+                }
                 self.windows.remove(&window_id);
             }
         }
@@ -112,20 +131,12 @@ impl ApplicationHandler<UserEvent> for App {
 
 pub trait AppWindow {
     fn id(&self) -> WindowId;
-    fn init(&mut self);
     fn handle_event(&mut self, event_loop: &ActiveEventLoop, event: &Event<UserEvent>);
 }
 
+#[derive(Debug)]
 pub enum UserEvent {
-    OpenWindow(Box<dyn AppWindow>),
-    CloseWindow(WindowId),
-}
-
-impl Debug for UserEvent {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Self::OpenWindow(window) => f.debug_tuple("OpenWindow").field(&window.id()).finish(),
-            Self::CloseWindow(window_id) => f.debug_tuple("CloseWindow").field(window_id).finish(),
-        }
-    }
+    OpenInputWindow,
+    OpenPlayer2Window,
+    Close(WindowId),
 }
diff --git a/src/app/game.rs b/src/app/game.rs
index efbeae0..ad3f6af 100644
--- a/src/app/game.rs
+++ b/src/app/game.rs
@@ -1,7 +1,4 @@
-use std::{
-    sync::{Arc, RwLock},
-    time::Instant,
-};
+use std::{sync::Arc, time::Instant};
 use wgpu::util::DeviceExt as _;
 use winit::{
     dpi::LogicalSize,
@@ -11,24 +8,22 @@ use winit::{
 };
 
 use crate::{
-    emulator::{EmulatorClient, EmulatorCommand},
-    input::InputMapper,
+    emulator::{EmulatorClient, EmulatorCommand, SimId},
     renderer::GameRenderer,
 };
 
 use super::{
     common::{ImguiState, WindowState, WindowStateBuilder},
-    input::InputWindow,
     AppWindow, UserEvent,
 };
 
 pub struct GameWindow {
     window: WindowState,
-    imgui: Option<ImguiState>,
+    imgui: ImguiState,
     pipeline: wgpu::RenderPipeline,
     bind_group: wgpu::BindGroup,
+    sim_id: SimId,
     client: EmulatorClient,
-    input_mapper: Arc<RwLock<InputMapper>>,
     proxy: EventLoopProxy<UserEvent>,
     paused_due_to_minimize: bool,
 }
@@ -36,21 +31,29 @@ pub struct GameWindow {
 impl GameWindow {
     pub fn new(
         event_loop: &ActiveEventLoop,
+        sim_id: SimId,
         client: EmulatorClient,
-        input_mapper: Arc<RwLock<InputMapper>>,
         proxy: EventLoopProxy<UserEvent>,
     ) -> Self {
+        let title = if sim_id == SimId::Player2 {
+            "Shrooms VB (Player 2)"
+        } else {
+            "Shrooms VB"
+        };
         let window = WindowStateBuilder::new(event_loop)
-            .with_title("Shrooms VB")
+            .with_title(title)
             .with_inner_size(LogicalSize::new(384, 244))
             .build();
         let device = &window.device;
 
         let eyes = Arc::new(GameRenderer::create_texture(device, "eye"));
-        client.send_command(EmulatorCommand::SetRenderer(GameRenderer {
-            queue: window.queue.clone(),
-            eyes: eyes.clone(),
-        }));
+        client.send_command(EmulatorCommand::SetRenderer(
+            sim_id,
+            GameRenderer {
+                queue: window.queue.clone(),
+                eyes: eyes.clone(),
+            },
+        ));
         let eyes = eyes.create_view(&wgpu::TextureViewDescriptor::default());
         let sampler = device.create_sampler(&wgpu::SamplerDescriptor::default());
         let colors = Colors {
@@ -158,13 +161,15 @@ impl GameWindow {
             cache: None,
         });
 
+        let imgui = ImguiState::new(&window);
+
         Self {
             window,
-            imgui: None,
+            imgui,
             pipeline: render_pipeline,
             bind_group,
+            sim_id,
             client,
-            input_mapper,
             proxy,
             paused_due_to_minimize: false,
         }
@@ -172,7 +177,7 @@ impl GameWindow {
 
     fn draw(&mut self, event_loop: &ActiveEventLoop) {
         let window = &mut self.window;
-        let imgui = self.imgui.as_mut().unwrap();
+        let imgui = &mut self.imgui;
         let mut context = imgui.context.lock().unwrap();
         let mut new_size = None;
 
@@ -204,7 +209,8 @@ impl GameWindow {
                         .show_open_single_file()
                         .unwrap();
                     if let Some(path) = rom {
-                        self.client.send_command(EmulatorCommand::LoadGame(path));
+                        self.client
+                            .send_command(EmulatorCommand::LoadGame(self.sim_id, path));
                     }
                 }
                 if ui.menu_item("Quit") {
@@ -240,14 +246,14 @@ impl GameWindow {
             });
             ui.menu("Input", || {
                 if ui.menu_item("Bind Inputs") {
-                    let input_window = Box::new(InputWindow::new(
-                        event_loop,
-                        self.input_mapper.clone(),
-                        self.proxy.clone(),
-                    ));
-                    self.proxy
-                        .send_event(UserEvent::OpenWindow(input_window))
-                        .unwrap();
+                    self.proxy.send_event(UserEvent::OpenInputWindow).unwrap();
+                }
+            });
+            ui.menu("Multiplayer", || {
+                if self.sim_id == SimId::Player1 && ui.menu_item("Open Player 2") {
+                    self.client
+                        .send_command(EmulatorCommand::StartSecondSim(None));
+                    self.proxy.send_event(UserEvent::OpenPlayer2Window).unwrap();
                 }
             });
         });
@@ -321,11 +327,6 @@ impl AppWindow for GameWindow {
         self.window.window.id()
     }
 
-    fn init(&mut self) {
-        self.imgui = Some(ImguiState::new(&self.window));
-        self.window.window.request_redraw();
-    }
-
     fn handle_event(&mut self, event_loop: &ActiveEventLoop, event: &Event<UserEvent>) {
         match event {
             Event::WindowEvent { event, .. } => match event {
@@ -341,7 +342,14 @@ impl AppWindow for GameWindow {
                         self.paused_due_to_minimize = false;
                     }
                 }
-                WindowEvent::CloseRequested => event_loop.exit(),
+                WindowEvent::CloseRequested => {
+                    if self.sim_id == SimId::Player2 {
+                        self.client.send_command(EmulatorCommand::StopSecondSim);
+                        self.proxy.send_event(UserEvent::Close(self.id())).unwrap();
+                    } else {
+                        event_loop.exit();
+                    }
+                }
                 WindowEvent::RedrawRequested => self.draw(event_loop),
                 _ => (),
             },
@@ -351,9 +359,7 @@ impl AppWindow for GameWindow {
             _ => (),
         }
         let window = &self.window;
-        let Some(imgui) = self.imgui.as_mut() else {
-            return;
-        };
+        let imgui = &mut self.imgui;
         let mut context = imgui.context.lock().unwrap();
         imgui
             .platform
diff --git a/src/app/input.rs b/src/app/input.rs
index d5ffe7e..b39f8b1 100644
--- a/src/app/input.rs
+++ b/src/app/input.rs
@@ -7,10 +7,12 @@ use winit::{
     dpi::LogicalSize,
     event::{Event, KeyEvent, WindowEvent},
     event_loop::{ActiveEventLoop, EventLoopProxy},
-    platform::modifier_supplement::KeyEventExtModifierSupplement,
 };
 
-use crate::{input::InputMapper, shrooms_vb_core::VBKey};
+use crate::{
+    emulator::{SimId, VBKey},
+    input::InputMapper,
+};
 
 use super::{
     common::{ImguiState, UiExt, WindowState, WindowStateBuilder},
@@ -19,10 +21,10 @@ use super::{
 
 pub struct InputWindow {
     window: WindowState,
-    imgui: Option<ImguiState>,
+    imgui: ImguiState,
     input_mapper: Arc<RwLock<InputMapper>>,
     proxy: EventLoopProxy<UserEvent>,
-    now_binding: Option<VBKey>,
+    now_binding: Option<(SimId, VBKey)>,
 }
 
 const KEY_NAMES: [(VBKey, &str); 14] = [
@@ -52,9 +54,10 @@ impl InputWindow {
             .with_title("Bind Inputs")
             .with_inner_size(LogicalSize::new(600, 400))
             .build();
+        let imgui = ImguiState::new(&window);
         Self {
             window,
-            imgui: None,
+            imgui,
             input_mapper,
             now_binding: None,
             proxy,
@@ -63,7 +66,7 @@ impl InputWindow {
 
     fn draw(&mut self) {
         let window = &mut self.window;
-        let imgui = self.imgui.as_mut().unwrap();
+        let imgui = &mut self.imgui;
         let mut context = imgui.context.lock().unwrap();
 
         let now = Instant::now();
@@ -85,11 +88,11 @@ impl InputWindow {
             .expect("Failed to prepare frame");
         let ui = context.new_frame();
 
-        let mut render_key_bindings = || {
+        let mut render_key_bindings = |sim_id: SimId| {
             if let Some(table) = ui.begin_table("controls", 2) {
                 let binding_names = {
                     let mapper = self.input_mapper.read().unwrap();
-                    mapper.binding_names()
+                    mapper.binding_names(&sim_id)
                 };
                 ui.table_next_row();
 
@@ -100,20 +103,20 @@ impl InputWindow {
                     ui.group(|| {
                         ui.right_align_text(name, space * 0.20);
                         ui.same_line();
-                        let label_text = if self.now_binding == Some(key) {
+                        let label_text = if self.now_binding == Some((sim_id, key)) {
                             "Press any input"
                         } else {
                             binding.unwrap_or("")
                         };
                         let label = format!("{}##{}", label_text, name);
                         if ui.button_with_size(label, [space * 0.60, 0.0]) {
-                            self.now_binding = Some(key);
+                            self.now_binding = Some((sim_id, key));
                         }
                     });
                     ui.same_line();
                     if ui.button(format!("Clear##{name}")) {
                         let mut mapper = self.input_mapper.write().unwrap();
-                        mapper.clear_binding(key);
+                        mapper.clear_binding(sim_id, key);
                     }
                 }
 
@@ -124,7 +127,11 @@ impl InputWindow {
         if let Some(window) = ui.fullscreen_window() {
             if let Some(tabs) = ui.tab_bar("tabs") {
                 if let Some(tab) = ui.tab_item("Player 1") {
-                    render_key_bindings();
+                    render_key_bindings(SimId::Player1);
+                    tab.end();
+                }
+                if let Some(tab) = ui.tab_item("Player 2") {
+                    render_key_bindings(SimId::Player2);
                     tab.end();
                 }
                 tabs.end();
@@ -175,11 +182,11 @@ impl InputWindow {
         if !event.state.is_pressed() {
             return;
         }
-        let Some(vb) = self.now_binding.take() else {
+        let Some((sim_id, vb)) = self.now_binding.take() else {
             return;
         };
         let mut mapper = self.input_mapper.write().unwrap();
-        mapper.bind_key(vb, event.key_without_modifiers());
+        mapper.bind_key(sim_id, vb, event.physical_key);
     }
 }
 
@@ -188,19 +195,13 @@ impl AppWindow for InputWindow {
         self.window.window.id()
     }
 
-    fn init(&mut self) {
-        self.imgui = Some(ImguiState::new(&self.window));
-        self.window.window.request_redraw();
-    }
-
     fn handle_event(&mut self, _: &ActiveEventLoop, event: &Event<UserEvent>) {
         match event {
             Event::WindowEvent { event, .. } => match event {
                 WindowEvent::Resized(size) => self.window.handle_resize(size),
-                WindowEvent::CloseRequested => self
-                    .proxy
-                    .send_event(UserEvent::CloseWindow(self.id()))
-                    .unwrap(),
+                WindowEvent::CloseRequested => {
+                    self.proxy.send_event(UserEvent::Close(self.id())).unwrap()
+                }
                 WindowEvent::KeyboardInput { event, .. } => self.try_bind_key(event),
                 WindowEvent::RedrawRequested => self.draw(),
                 _ => (),
@@ -212,9 +213,7 @@ impl AppWindow for InputWindow {
         }
 
         let window = &self.window;
-        let Some(imgui) = self.imgui.as_mut() else {
-            return;
-        };
+        let imgui = &mut self.imgui;
         let mut context = imgui.context.lock().unwrap();
         imgui
             .platform
diff --git a/src/controller.rs b/src/controller.rs
index 70861ab..d10a1ab 100644
--- a/src/controller.rs
+++ b/src/controller.rs
@@ -2,48 +2,46 @@ use std::sync::{Arc, RwLock};
 
 use winit::event::{ElementState, KeyEvent};
 
-use crate::{input::InputMapper, shrooms_vb_core::VBKey};
+use crate::{
+    emulator::{SimId, VBKey},
+    input::InputMapper,
+};
 
 pub struct ControllerState {
     input_mapper: Arc<RwLock<InputMapper>>,
-    pressed: VBKey,
+    pressed: Vec<VBKey>,
 }
 
 impl ControllerState {
     pub fn new(input_mapper: Arc<RwLock<InputMapper>>) -> Self {
         Self {
             input_mapper,
-            pressed: VBKey::SGN,
+            pressed: vec![VBKey::SGN; 2],
         }
     }
 
-    pub fn pressed(&self) -> VBKey {
-        self.pressed
-    }
-
-    pub fn key_event(&mut self, event: &KeyEvent) -> bool {
-        let Some(input) = self.key_event_to_input(event) else {
-            return false;
-        };
+    pub fn key_event(&mut self, event: &KeyEvent) -> Option<(SimId, VBKey)> {
+        let (sim_id, input) = self.key_event_to_input(event)?;
+        let pressed = &mut self.pressed[sim_id.to_index()];
         match event.state {
             ElementState::Pressed => {
-                if self.pressed.contains(input) {
-                    return false;
+                if pressed.contains(input) {
+                    return None;
                 }
-                self.pressed.insert(input);
-                true
+                pressed.insert(input);
+                Some((sim_id, *pressed))
             }
             ElementState::Released => {
-                if !self.pressed.contains(input) {
-                    return false;
+                if !pressed.contains(input) {
+                    return None;
                 }
-                self.pressed.remove(input);
-                true
+                pressed.remove(input);
+                Some((sim_id, *pressed))
             }
         }
     }
 
-    fn key_event_to_input(&self, event: &KeyEvent) -> Option<VBKey> {
+    fn key_event_to_input(&self, event: &KeyEvent) -> Option<(SimId, VBKey)> {
         let mapper = self.input_mapper.read().unwrap();
         mapper.key_event(event)
     }
diff --git a/src/emulator.rs b/src/emulator.rs
index 38fdab6..4bb8386 100644
--- a/src/emulator.rs
+++ b/src/emulator.rs
@@ -1,4 +1,5 @@
 use std::{
+    collections::HashMap,
     fs,
     path::{Path, PathBuf},
     sync::{
@@ -10,11 +11,11 @@ use std::{
 
 use anyhow::Result;
 
-use crate::{
-    audio::Audio,
-    renderer::GameRenderer,
-    shrooms_vb_core::{CoreVB, VBKey},
-};
+use crate::{audio::Audio, renderer::GameRenderer};
+use shrooms_vb_core::Sim;
+pub use shrooms_vb_core::VBKey;
+
+mod shrooms_vb_core;
 
 pub struct EmulatorBuilder {
     rom: Option<PathBuf>,
@@ -23,6 +24,20 @@ pub struct EmulatorBuilder {
     has_game: Arc<AtomicBool>,
 }
 
+#[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
+pub enum SimId {
+    Player1,
+    Player2,
+}
+impl SimId {
+    pub fn to_index(self) -> usize {
+        match self {
+            Self::Player1 => 0,
+            Self::Player2 => 1,
+        }
+    }
+}
+
 impl EmulatorBuilder {
     pub fn new() -> (Self, EmulatorClient) {
         let (queue, commands) = mpsc::channel();
@@ -50,17 +65,17 @@ impl EmulatorBuilder {
     pub fn build(self) -> Result<Emulator> {
         let mut emulator = Emulator::new(self.commands, self.running, self.has_game)?;
         if let Some(path) = self.rom {
-            emulator.load_rom(&path)?;
+            emulator.load_rom_from_file(SimId::Player1, &path)?;
         }
         Ok(emulator)
     }
 }
 
 pub struct Emulator {
-    sim: CoreVB,
+    sims: Vec<Sim>,
     audio: Audio,
     commands: mpsc::Receiver<EmulatorCommand>,
-    renderer: Option<GameRenderer>,
+    renderers: HashMap<SimId, GameRenderer>,
     running: Arc<AtomicBool>,
     has_game: Arc<AtomicBool>,
 }
@@ -72,24 +87,50 @@ impl Emulator {
         has_game: Arc<AtomicBool>,
     ) -> Result<Self> {
         Ok(Self {
-            sim: CoreVB::new(),
+            sims: vec![],
             audio: Audio::init()?,
             commands,
-            renderer: None,
+            renderers: HashMap::new(),
             running,
             has_game,
         })
     }
 
-    pub fn load_rom(&mut self, path: &Path) -> Result<()> {
+    pub fn load_rom_from_file(&mut self, sim_id: SimId, path: &Path) -> Result<()> {
         let bytes = fs::read(path)?;
-        self.sim.reset();
-        self.sim.load_rom(bytes)?;
+        self.load_rom(sim_id, bytes)?;
+        Ok(())
+    }
+
+    pub fn start_second_sim(&mut self, rom: Option<PathBuf>) -> Result<()> {
+        let bytes = if let Some(path) = rom {
+            fs::read(path)?
+        } else if let Some(rom) = self.sims.first().and_then(|s| s.clone_rom()) {
+            rom
+        } else {
+            return Ok(());
+        };
+        self.load_rom(SimId::Player2, bytes)?;
+        Ok(())
+    }
+
+    fn load_rom(&mut self, sim_id: SimId, bytes: Vec<u8>) -> Result<()> {
+        while self.sims.len() <= sim_id.to_index() {
+            self.sims.push(Sim::new());
+        }
+        let sim = &mut self.sims[sim_id.to_index()];
+        sim.reset();
+        sim.load_rom(bytes)?;
         self.has_game.store(true, Ordering::Release);
         self.running.store(true, Ordering::Release);
         Ok(())
     }
 
+    pub fn stop_second_sim(&mut self) {
+        self.renderers.remove(&SimId::Player2);
+        self.sims.truncate(1);
+    }
+
     pub fn run(&mut self) {
         let mut eye_contents = vec![0u8; 384 * 224 * 2];
         let mut audio_samples = vec![];
@@ -97,15 +138,20 @@ impl Emulator {
             let mut idle = true;
             if self.running.load(Ordering::Acquire) {
                 idle = false;
-                self.sim.emulate_frame();
+                Sim::emulate_many(&mut self.sims);
             }
-            if let Some(renderer) = &mut self.renderer {
-                if self.sim.read_pixels(&mut eye_contents) {
-                    idle = false;
-                    renderer.render(&eye_contents);
+            for (sim_id, renderer) in self.renderers.iter_mut() {
+                if let Some(sim) = self.sims.get_mut(sim_id.to_index()) {
+                    if sim.read_pixels(&mut eye_contents) {
+                        idle = false;
+                        renderer.render(&eye_contents);
+                    }
                 }
             }
-            self.sim.read_samples(&mut audio_samples);
+            let weight = 1.0 / self.sims.len() as f32;
+            for sim in self.sims.iter_mut() {
+                sim.read_samples(&mut audio_samples, weight);
+            }
             if !audio_samples.is_empty() {
                 idle = false;
                 self.audio.update(&audio_samples);
@@ -137,14 +183,22 @@ impl Emulator {
 
     fn handle_command(&mut self, command: EmulatorCommand) {
         match command {
-            EmulatorCommand::SetRenderer(renderer) => {
-                self.renderer = Some(renderer);
+            EmulatorCommand::SetRenderer(sim_id, renderer) => {
+                self.renderers.insert(sim_id, renderer);
             }
-            EmulatorCommand::LoadGame(path) => {
-                if let Err(error) = self.load_rom(&path) {
+            EmulatorCommand::LoadGame(sim_id, path) => {
+                if let Err(error) = self.load_rom_from_file(sim_id, &path) {
                     eprintln!("error loading rom: {}", error);
                 }
             }
+            EmulatorCommand::StartSecondSim(path) => {
+                if let Err(error) = self.start_second_sim(path) {
+                    eprintln!("error starting second sim: {}", error);
+                }
+            }
+            EmulatorCommand::StopSecondSim => {
+                self.stop_second_sim();
+            }
             EmulatorCommand::Pause => {
                 self.running.store(false, Ordering::Release);
             }
@@ -154,11 +208,17 @@ impl Emulator {
                 }
             }
             EmulatorCommand::Reset => {
-                self.sim.reset();
-                self.running.store(true, Ordering::Release);
+                for sim in self.sims.iter_mut() {
+                    sim.reset();
+                }
+                if !self.sims.is_empty() {
+                    self.running.store(true, Ordering::Release);
+                }
             }
-            EmulatorCommand::SetKeys(keys) => {
-                self.sim.set_keys(keys);
+            EmulatorCommand::SetKeys(sim_id, keys) => {
+                if let Some(sim) = self.sims.get_mut(sim_id.to_index()) {
+                    sim.set_keys(keys);
+                }
             }
         }
     }
@@ -166,12 +226,14 @@ impl Emulator {
 
 #[derive(Debug)]
 pub enum EmulatorCommand {
-    SetRenderer(GameRenderer),
-    LoadGame(PathBuf),
+    SetRenderer(SimId, GameRenderer),
+    LoadGame(SimId, PathBuf),
+    StartSecondSim(Option<PathBuf>),
+    StopSecondSim,
     Pause,
     Resume,
     Reset,
-    SetKeys(VBKey),
+    SetKeys(SimId, VBKey),
 }
 
 #[derive(Clone)]
diff --git a/src/shrooms_vb_core.rs b/src/emulator/shrooms_vb_core.rs
similarity index 83%
rename from src/shrooms_vb_core.rs
rename to src/emulator/shrooms_vb_core.rs
index 324689d..507085e 100644
--- a/src/shrooms_vb_core.rs
+++ b/src/emulator/shrooms_vb_core.rs
@@ -25,6 +25,12 @@ enum VBDataType {
     F32 = 5,
 }
 
+#[repr(i32)]
+#[derive(FromPrimitive, ToPrimitive)]
+enum VBOption {
+    PseudoHalt = 0,
+}
+
 bitflags! {
     #[repr(transparent)]
     #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
@@ -52,8 +58,8 @@ type OnFrame = extern "C" fn(sim: *mut VB) -> c_int;
 
 #[link(name = "vb")]
 extern "C" {
-    #[link_name = "vbEmulate"]
-    fn vb_emulate(sim: *mut VB, cycles: *mut u32) -> c_int;
+    #[link_name = "vbEmulateEx"]
+    fn vb_emulate_ex(sims: *mut *mut VB, count: c_uint, cycles: *mut u32) -> c_int;
     #[link_name = "vbGetCartROM"]
     fn vb_get_cart_rom(sim: *mut VB, size: *mut u32) -> *mut c_void;
     #[link_name = "vbGetPixels"]
@@ -81,10 +87,12 @@ extern "C" {
     fn vb_reset(sim: *mut VB);
     #[link_name = "vbSetCartROM"]
     fn vb_set_cart_rom(sim: *mut VB, rom: *mut c_void, size: u32) -> c_int;
-    #[link_name = "vbSetKeys"]
-    fn vb_set_keys(sim: *mut VB, keys: u16) -> u16;
     #[link_name = "vbSetFrameCallback"]
     fn vb_set_frame_callback(sim: *mut VB, on_frame: OnFrame);
+    #[link_name = "vbSetKeys"]
+    fn vb_set_keys(sim: *mut VB, keys: u16) -> u16;
+    #[link_name = "vbSetOption"]
+    fn vb_set_option(sim: *mut VB, key: VBOption, value: c_int);
     #[link_name = "vbSetSamples"]
     fn vb_set_samples(
         sim: *mut VB,
@@ -113,14 +121,15 @@ struct VBState {
     frame_seen: bool,
 }
 
-pub struct CoreVB {
+#[repr(transparent)]
+pub struct Sim {
     sim: *mut VB,
 }
 
 // SAFETY: the memory pointed to by sim is valid
-unsafe impl Send for CoreVB {}
+unsafe impl Send for Sim {}
 
-impl CoreVB {
+impl Sim {
     pub fn new() -> Self {
         // init the VB instance itself
         let size = unsafe { vb_size_of() };
@@ -128,6 +137,7 @@ impl CoreVB {
         let memory = vec![0u64; size.div_ceil(4)];
         let sim: *mut VB = Box::into_raw(memory.into_boxed_slice()).cast();
         unsafe { vb_init(sim) };
+        unsafe { vb_set_option(sim, VBOption::PseudoHalt, 1) };
         unsafe { vb_reset(sim) };
 
         // set up userdata
@@ -140,7 +150,7 @@ impl CoreVB {
         let samples: *mut c_void = Box::into_raw(audio_buffer.into_boxed_slice()).cast();
         unsafe { vb_set_samples(sim, samples, VBDataType::F32, AUDIO_CAPACITY_SAMPLES as u32) };
 
-        CoreVB { sim }
+        Sim { sim }
     }
 
     pub fn reset(&mut self) {
@@ -162,6 +172,17 @@ impl CoreVB {
         }
     }
 
+    pub fn clone_rom(&self) -> Option<Vec<u8>> {
+        let mut size = 0;
+        let rom = unsafe { vb_get_cart_rom(self.sim, &mut size) };
+        if rom.is_null() {
+            return None;
+        }
+        // SAFETY: rom definitely points to a valid array of `size` bytes
+        let slice: &[u8] = unsafe { slice::from_raw_parts(rom.cast(), size as usize) };
+        Some(slice.to_vec())
+    }
+
     fn unload_rom(&mut self) -> Option<Vec<u8>> {
         let mut size = 0;
         let rom = unsafe { vb_get_cart_rom(self.sim, &mut size) };
@@ -173,9 +194,11 @@ impl CoreVB {
         Some(vec)
     }
 
-    pub fn emulate_frame(&mut self) {
+    pub fn emulate_many(sims: &mut [Sim]) {
         let mut cycles = 20_000_000;
-        unsafe { vb_emulate(self.sim, &mut cycles) };
+        let count = sims.len() as c_uint;
+        let sims = sims.as_mut_ptr().cast();
+        unsafe { vb_emulate_ex(sims, count, &mut cycles) };
     }
 
     pub fn read_pixels(&mut self, buffers: &mut [u8]) -> bool {
@@ -203,14 +226,17 @@ impl CoreVB {
         true
     }
 
-    pub fn read_samples(&mut self, samples: &mut Vec<f32>) {
+    pub fn read_samples(&mut self, samples: &mut Vec<f32>, weight: f32) {
         let mut position = 0;
         let ptr =
             unsafe { vb_get_samples(self.sim, ptr::null_mut(), ptr::null_mut(), &mut position) };
         // SAFETY: position is an offset in a buffer of (f32, f32). so, position * 2 is an offset in a buffer of f32.
-        let read_samples: &mut [f32] =
-            unsafe { slice::from_raw_parts_mut(ptr.cast(), position as usize * 2) };
-        samples.extend_from_slice(read_samples);
+        let read_samples: &[f32] =
+            unsafe { slice::from_raw_parts(ptr.cast(), position as usize * 2) };
+        samples.resize(read_samples.len(), 0.0);
+        for (index, sample) in read_samples.iter().enumerate() {
+            samples[index] += sample * weight;
+        }
 
         unsafe {
             vb_set_samples(
@@ -227,7 +253,7 @@ impl CoreVB {
     }
 }
 
-impl Drop for CoreVB {
+impl Drop for Sim {
     fn drop(&mut self) {
         let ptr =
             unsafe { vb_get_samples(self.sim, ptr::null_mut(), ptr::null_mut(), ptr::null_mut()) };
diff --git a/src/input.rs b/src/input.rs
index 5367d60..44e626e 100644
--- a/src/input.rs
+++ b/src/input.rs
@@ -2,15 +2,14 @@ use std::collections::HashMap;
 
 use winit::{
     event::KeyEvent,
-    keyboard::{Key, NamedKey},
-    platform::modifier_supplement::KeyEventExtModifierSupplement,
+    keyboard::{KeyCode, PhysicalKey},
 };
 
-use crate::shrooms_vb_core::VBKey;
+use crate::emulator::{SimId, VBKey};
 
 pub struct InputMapper {
-    vb_bindings: HashMap<VBKey, Key>,
-    key_bindings: HashMap<Key, VBKey>,
+    vb_bindings: HashMap<SimId, HashMap<VBKey, PhysicalKey>>,
+    key_bindings: HashMap<PhysicalKey, (SimId, VBKey)>,
 }
 
 impl InputMapper {
@@ -19,30 +18,48 @@ impl InputMapper {
             vb_bindings: HashMap::new(),
             key_bindings: HashMap::new(),
         };
-        mapper.bind_key(VBKey::SEL, Key::Character("a".into()));
-        mapper.bind_key(VBKey::STA, Key::Character("s".into()));
-        mapper.bind_key(VBKey::B, Key::Character("d".into()));
-        mapper.bind_key(VBKey::A, Key::Character("f".into()));
-        mapper.bind_key(VBKey::LT, Key::Character("e".into()));
-        mapper.bind_key(VBKey::RT, Key::Character("r".into()));
-        mapper.bind_key(VBKey::RU, Key::Character("i".into()));
-        mapper.bind_key(VBKey::RL, Key::Character("j".into()));
-        mapper.bind_key(VBKey::RD, Key::Character("k".into()));
-        mapper.bind_key(VBKey::RR, Key::Character("l".into()));
-        mapper.bind_key(VBKey::LU, Key::Named(NamedKey::ArrowUp));
-        mapper.bind_key(VBKey::LL, Key::Named(NamedKey::ArrowLeft));
-        mapper.bind_key(VBKey::LD, Key::Named(NamedKey::ArrowDown));
-        mapper.bind_key(VBKey::LR, Key::Named(NamedKey::ArrowRight));
+        mapper.bind_key(SimId::Player1, VBKey::SEL, PhysicalKey::Code(KeyCode::KeyA));
+        mapper.bind_key(SimId::Player1, VBKey::STA, PhysicalKey::Code(KeyCode::KeyS));
+        mapper.bind_key(SimId::Player1, VBKey::B, PhysicalKey::Code(KeyCode::KeyD));
+        mapper.bind_key(SimId::Player1, VBKey::A, PhysicalKey::Code(KeyCode::KeyF));
+        mapper.bind_key(SimId::Player1, VBKey::LT, PhysicalKey::Code(KeyCode::KeyE));
+        mapper.bind_key(SimId::Player1, VBKey::RT, PhysicalKey::Code(KeyCode::KeyR));
+        mapper.bind_key(SimId::Player1, VBKey::RU, PhysicalKey::Code(KeyCode::KeyI));
+        mapper.bind_key(SimId::Player1, VBKey::RL, PhysicalKey::Code(KeyCode::KeyJ));
+        mapper.bind_key(SimId::Player1, VBKey::RD, PhysicalKey::Code(KeyCode::KeyK));
+        mapper.bind_key(SimId::Player1, VBKey::RR, PhysicalKey::Code(KeyCode::KeyL));
+        mapper.bind_key(
+            SimId::Player1,
+            VBKey::LU,
+            PhysicalKey::Code(KeyCode::ArrowUp),
+        );
+        mapper.bind_key(
+            SimId::Player1,
+            VBKey::LL,
+            PhysicalKey::Code(KeyCode::ArrowLeft),
+        );
+        mapper.bind_key(
+            SimId::Player1,
+            VBKey::LD,
+            PhysicalKey::Code(KeyCode::ArrowDown),
+        );
+        mapper.bind_key(
+            SimId::Player1,
+            VBKey::LR,
+            PhysicalKey::Code(KeyCode::ArrowRight),
+        );
         mapper
     }
 
-    pub fn binding_names(&self) -> HashMap<VBKey, String> {
-        self.vb_bindings
+    pub fn binding_names(&self, sim_id: &SimId) -> HashMap<VBKey, String> {
+        let Some(bindings) = self.vb_bindings.get(sim_id) else {
+            return HashMap::new();
+        };
+        bindings
             .iter()
             .map(|(k, v)| {
                 let name = match v {
-                    Key::Character(char) => char.to_string(),
-                    Key::Named(key) => format!("{:?}", key),
+                    PhysicalKey::Code(code) => format!("{code:?}"),
                     k => format!("{:?}", k),
                 };
                 (*k, name)
@@ -50,22 +67,22 @@ impl InputMapper {
             .collect()
     }
 
-    pub fn bind_key(&mut self, vb: VBKey, key: Key) {
-        if let Some(old) = self.vb_bindings.insert(vb, key.clone()) {
+    pub fn bind_key(&mut self, sim_id: SimId, vb: VBKey, key: PhysicalKey) {
+        let vb_bindings = self.vb_bindings.entry(sim_id).or_default();
+        if let Some(old) = vb_bindings.insert(vb, key) {
             self.key_bindings.remove(&old);
         }
-        self.key_bindings.insert(key, vb);
+        self.key_bindings.insert(key, (sim_id, vb));
     }
 
-    pub fn clear_binding(&mut self, vb: VBKey) {
-        if let Some(old) = self.vb_bindings.remove(&vb) {
+    pub fn clear_binding(&mut self, sim_id: SimId, vb: VBKey) {
+        let vb_bindings = self.vb_bindings.entry(sim_id).or_default();
+        if let Some(old) = vb_bindings.remove(&vb) {
             self.key_bindings.remove(&old);
         }
     }
 
-    pub fn key_event(&self, event: &KeyEvent) -> Option<VBKey> {
-        self.key_bindings
-            .get(&event.key_without_modifiers())
-            .cloned()
+    pub fn key_event(&self, event: &KeyEvent) -> Option<(SimId, VBKey)> {
+        self.key_bindings.get(&event.physical_key).copied()
     }
 }
diff --git a/src/main.rs b/src/main.rs
index b8de1cf..9297ee4 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -13,7 +13,6 @@ mod controller;
 mod emulator;
 mod input;
 mod renderer;
-mod shrooms_vb_core;
 
 #[derive(Parser)]
 struct Args {