Savage Wombat
Hero
AngryDM had an article about this when 5e was in development. Basically, he agrees that they're "trap monsters", or better yet "puzzle monsters" - and that a lot of DMs do like them. But, as Hussar said, if you want to use them as puzzles you have to play fair, and that means giving clues. Not, say, suddenly teleporting 4 medusae with assassin levels to spots within 20' of the party.
