There's a cute flash game called Achievement Unlocked (I think) that should give you about 1,000 ideas.
Other ideas include getting down a staircase without killing anyone, making it through a whole level while using only one kind of trap, killing the final boss and self with the same trap... stuff like that... IIRC, the first two achievements are automatic given the limited supply of traps at the start of the game, so yes, tweaking.