Free to play · Available on itch.io and Discord

What if your heart rate was a game mechanic? Not just a number on a smartwatch - but something that directly shaped what you could see, how fast you played, and whether your team survived? That's exactly what Critter Core does.

Critter Core is a free, browser-based multiplayer maze deathmatch for up to 4 players. It runs in any modern browser, requires no download, and can be launched as a Discord Activity directly inside a voice channel. Whether you're competing with friends online or huddled in a Discord call, the game meets you where you already are.

What Is Critter Core?

At its core (pun intended), Critter Core is a top-down arena shooter set inside procedurally generated mazes. Every round the layout changes, so no two matches ever play out the same way. You move with WASD or arrow keys and fire rockets at opponents and monsters alike.

Up to four players can join a shared room — either through the browser version on itch.io or natively as a Discord Activity — and battle it out across three distinct game modes. The session server handles matchmaking, room management, and real-time game state, so all you need is a browser and an internet connection.

Three Game Modes, One Arena

🏰 Maze — Deathmatch

The classic mode. Eliminate opponents, survive monster waves, and climb the scoreboard. Every elimination earns you points; every death costs you. The maze reshuffles between rounds, keeping every match fresh and unpredictable.

♥️ Heart rate twist: Connect a heart rate monitor and your field of vision dynamically shrinks as your pulse rises. The calmer you stay, the more of the maze you can see. Panic — and the walls close in.

🔦 Control — Zone Capture

One zone. One winner. Stand inside the glowing capture point to claim it and score points over time. The catch: opponents can contest the zone by standing in it too, and only one team can hold it at a time.

♥️ Heart rate twist: A racing pulse slows your capture speed. The more wound up you are, the longer it takes to claim the zone — so take a breath, hold position, and outlast the competition.

🤝 Coop — Survive Together

Set aside the rivalry. In Coop mode, all players share the same goal: survive endless, increasingly aggressive monster waves. Coordination matters — who covers which corridor, when to retreat, how to share powerups.

♥️ Heart rate twist: Only the player with the lowest heart rate has full vision of the maze. Everyone else is navigating in the dark — but can ping their position so teammates can find them. The calmest player becomes the guide; everyone else has to trust them.

Heart Rate as a Game Mechanic — Powered by HypeRate

Critter Core integrates with HypeRate, a platform that streams live BPM data from smartwatches, chest straps, and fitness trackers directly into apps and games. Any HypeRate-compatible device works — Apple Watch, Garmin, Polar, and many more.

Once connected, your heart rate becomes a live game variable. It's not a gimmick — it's mechanically integrated into every mode differently, creating a meta-game around staying calm under pressure. Veteran FPS players who stay ice-cold under fire have a genuine advantage. Players who panic measurably pay for it.

Heart rate integration is entirely optional. Every mode is fully playable without a monitor — the BPM system simply adds a layer of depth for players who want it.

Play Without Leaving Discord

One of Critter Core's most distinctive features is its Discord Activity integration. Discord Activities are games and apps that run natively inside a voice channel — no links to share, no tabs to switch, no "hey, what's the URL again?" Just launch the Activity, and anyone in the channel can join instantly.

The Discord version includes full Rich Presence support: your game state (waiting in lobby, in a maze match, current score) appears on your Discord profile in real time. Friends can see what you're up to and jump in without asking.

The heart rate proxy for HypeRate also runs through the game server in Discord mode, working around the platform's content security policies so the BPM integration works seamlessly inside the Activity iframe.

Powerups That Change the Fight

Scattered throughout every maze are powerups that can flip a match in seconds:

• Wall Pierce — Rockets pass straight through maze walls
• Speed Boost — Move fast enough to outrun almost anything
• Invincibility — Shrug off incoming fire for a brief window
• Rapid Fire — Unleash a continuous barrage of rockets
• Homing Rocket — Fire and forget — missiles find their own targets

Grabbing the right powerup at the right moment is often the difference between first place and respawning. Knowing when to chase a powerup versus hold position is a skill in itself.

Monsters You'll Learn to Respect

Critter Core isn't just a PvP game — the maze is alive with monsters that pursue, flank, and split:

• Crawler — Predictable patrol routes, easy to avoid until there are four of them
• Stalker — Locks onto the nearest player and doesn't stop
• Phantom — Ignores walls entirely, making no corner safe
• Splitter — Destroying it spawns two smaller, faster minisplits

Monsters scale in aggression over time, so early rounds feel manageable while late-game waves become genuinely threatening — especially in Coop mode when vision is limited.

Free to Play — No Account Required

Critter Core is completely free. There's no account system, no login wall, and no download. Enter a name, optionally a Room ID to play privately with friends, and hit JOIN. The game handles the rest.

Private rooms work by entering a shared Room ID — anyone who types the same ID ends up in the same session. No invite links, no lobby codes to manage. Just agree on a name and play.

Where to Play

• Browser (itch.io): Play directly in your browser at itch.io — no download, works on any desktop browser.
• Discord Activity: Launch Critter Core from inside any Discord voice channel. Requires the Discord desktop or web app.

Final Thoughts

Critter Core sits at an interesting intersection: it's quick to pick up (jump in, shoot things, dodge monsters), but the heart rate layer gives it unusual depth that most browser games simply don't have. The Discord Activity integration makes it genuinely frictionless for groups who are already in a call together.

If you're looking for something to play with friends that doesn't require installs, accounts, or explaining rules for ten minutes — Critter Core is worth a try. Especially if you own a smartwatch and want to find out whether you're actually calm under pressure.

Spoiler: you're probably not.