Warp Dream, Warp Reality, Warp Nightmare - Any three rooms with warps.
Trespassing On Private Property - Firstly, in the beginning of the level, you can go into a room off of the main trail and see a room with many enemies and one trinket that you can access much later.
Up For A Challenge? - The first room in a set that will be a challenge, or a DTTHW joke. (You know, since you start by going up [or down])
I hope this helped a bit. No credit really needed.