In Episode 5, the numerous shape changing traps are hilarious, from rendering the characters as 8-bit sprites, to putting them in mascot outfits (with Kayaa as a Bunny Girl) - to a gender switching trap right in front of a hotspring (with a 8-bit strap right in front of the door).
The Roper dance. It's seen first in 8-bit, and then again in Duraga's art style (but fast-forwarded).
The long string of Retirony gags in the first episode. Even the villain gets in on it.