Out of ideas, well I got some... :?

[HTel]

I got one Idea using the multiplayer aspect of the gamebuino. I think (judging of what you guys have made) would be possible to play on the gamebuino (I hope you can understand my crappy version of code, but that is how specific I can get, by the way... I am not a FPS fan):

3D{i}
Multiplayer (2 players min, 4 players max, no teams){i}
[Press A when "Someone" is in area of vision, take 1 Hp(all vision) from opposing player;
Press A, remove 1 Ammo(local);
Walk past "Packs", set 10 Ammo(local);
Walk past "Packs", add 1 HP(local);
Press C, start pause menu;
Start game, add 10 HP(all)
Start game, add 10 Ammo(all)

[Sushi]

This would be easy in single player, but relatively hard for multiplayer. i2c is confuzzling(at least for me) and having a pause menu in multiplayer would mean that every player would have to pause, or it would be pause at your own risk. Try taking a look at the 2p pong code. It's pretty advanced.