How about this one: A group of rabbits is standing near a chest/flag/portal/something, when enough time has passed the floor will open and the defenders win.

Defenders have five lives and there will be coming attackers from both sides of the level.

Smth like this:
&&&&&&___________
&&&&&&l&&&&&&&&&l
&&A&&&l &&&&D&&&&l &&&A
&&&&&&W&&&C&&6&&W
_______________________

Where A=Attacker, D=Defender, W=Wall for the defenders and stop ammos, and C=the protected thing. & is a symbol.

You get the idea.