The Rabbit of Caerbannog
STR 5 (-3) | DEX 16 (+3) | CON 10 (+0) | INT 10 (+0) | WIS 14 (+2) | CHA 13 (+1)
HP 70 (30D4) | AC15 | Speed 40ft
Multiattack: Can make 2x Bite attacks
Jump: Can jump 20 feet. The target must make a DC16 Dex Save or be knocked prone, taking 2d4 blugeoning damage. If the target is knocked prone, make a bite attack.
Bite: +7 to hit, 2d6+3 piercing

Petrified Encounters

The infinite room 30ft cube room with a wooden door on each side a trap door in the middle of the floor and one on the roof. The room is has no furniture, there is skeleton in one corner and near the center of the room is the remanents of a camp fire with a corpse around 6months old and another body nearby with a cracked skull and charred bones Room Loot
-Leather backpack with bite marks
-A journal with entries that grow more maddening
-Blood stained hammer
-50ft rope
-pickaxe
-woodaxe
Entering any door will loop around to the door on the other side of the room, dropping through the trap door on the floor loops through to the trap door on the roof The only door that doesn't loop is entering the trap door on the roof.

Blood Wall: A large wall blocks the cave path, with writing on it. It can be in any language that is appropriate, best a language only one or two can read. On it is a poem, that goes:

"The key exists in side your head
use the key to paint me red
but be aware of what you spurn
for what was taken shall be returned"

The party has to paint the wall with blood (it can be interesting to see where they get it), and a version of whatever's blood you painted it with crawls out, and you have to defeat it to move on.
I thought of this after i realized the two most likely options my friends would take would be to paint it with dragons blood, or this one dick would cut the head off an npc. The creature's strength can be adjusted edit: the blood, once exposed, would shoot to the wall and slither into the words, glow, then sink away, then out comes the creature

Treasure room Solid stone, unbreakable. Theres a font of coins and treasure. As soon as the PCs touch the coins, they disappear and the room seals itself. Then an ethereal countdown begins. The lever on the wall over there looks like your only chance, so you flick it. The countdown resets but continues counting.
The trick? The countdown is counting down to the door unlocking. Nothing else. It just wastes time an their abilities as they try to get out.