Underused concepts?

[Hornlitz]

You have to stay clear for a bit, but the water is fine if you aren't there where the monster drowns, or shortly thereafter.

I'm not a fan of tight time limits, although there are a few where it works. Just a Minute is one of my favorites.

I think if the time limit is the point, then you limit the level in other ways (like not much sokoban or blobs).

Teeth/paramecium/bug cloners are underused because of the b/c glitch -- this can be worked around, and should be.

Also you can look at my BHLS2 level, Four Corners of the Earth. I used teeth on traps AND Paramecium on traps and it works perfectly.