You are the orange cat. You press WASD and space to move and attack. Green cats will spawn from the spawner and shoot at you. If your health reaches zero, you die. When you kill a green cat, it has a chance to drop a heart. The difficulty affects mob spawn time, shooting speed, and heart drop chance. Type your highest score in chat. May the odds be ever in your favor! I may add different weapons and maybe make it two-player. We shall see.
The cats and the background are Scratch default. The spawner and flame animations are based on Minecraft, but original art. I didn't copy any code.