Sometimes I think I can be a little gimmick-happy
but off the top of my head..
Artillery attacks
Laser sentries
lava pits (with tidal action!)
hypothermic water
intermittent steam jets
camouflaged walls that you can shoot people through
being trapped in a rocket blast chamber
platforms that start to sink when you step on them
Pretty much anything from a Mario game
just don't use all of those at once
