I am a fan of the Barrel of monkes trap; flavor it to be monkey skeletons, complete with tail.

Players are in a 3x3 room with a barrel in it. If a player decides to open the barrel, the door lock (magically and mechanically), and skeleton monkeys are infinitely spawned out of the barrel. 1 for the first round, 2 for the 2nd, etc. (maybe cap it at 5 jumping out per round). They will spawn infinitely until the barrel lid is closed. If they don't figure this out in time they will literally be crushed to death after a while.

Strength check to determine if the PC is strong enough to close the lid with monkeys jumping out. DC based on how many monkeys are jumping out per round.

If they break the lid, they make the strength check at disadvantage since now they have to close the barrel using two halves of a lid.

Barrel can be destroyed, but if that happens all the current monkey skeletons in the room become hostile (they are not otherwise unless directly attacked) and an encounter happens.