Found a super-secret room with what looks like an unintended grub jump requirement. That is, a 1-height passage with a block under the entrance but not the exit. The power-up at the end of the room was Damage x2. I was able to make it to the damage power-up, but couldn't make it all the way back out.
Unfortunately, what was under the passage exit was spikes, so I ded, and couldn't screenshot >_<.
The set of relevant power-ups I had were:
- Lava suit
- Grub suit