D&D 5E Your Personal Favorite "Old School" Monsters

[Li Shenron]

Bronze Golem, Rust Monster, various Oozes... basically monsters which had a trick up their sleeve that made your first combat strategy (usually: just attack them) a bad idea, and forced you to find another way. Of course nowadays everybody knows what to expect from those monsters and can adapt since first round, but back then they worked.

 

[jasper]

Mrs. Grey 6 foot 6 Homeroom teacher with a four foot yard stick. Once straight lifted the class problem child. Brought him and his desk up to eye level. Said, "Behave!" Dropped the desk with him in it. He behaved for a week after that. (ca 1976)

 

[ccs]

5 favorites:
Grell - that full page pic in the 1e FF.... Imagine creeping around in a dungeon & encountering that thing!
Displacer Beasts - they've just always grabbed my imagination
Hook Horrors - as they appear in 1e. So cool looking. Especially that old LJN toy from the 80's
Osquips - sure, basically just dire rats. But so much cooler looking!
Hydra - a vastly underused true classic.....

*Another creature that's always stuck in my imagination: the Ass-were.
Yes, an evil lycanthropic donkey. I forget where it came from (2e?) I'd LOVE to see someone make an quality adventure around this thing. Maybe a murder mystery? I mean, who'd ever suspect the pack animal?
Why haven't I ever used it? 1) I'm not that good at writing mysteries. 2) Most of the groups I've played with aren't that big on playing mysteries &/or are terrible at solving them. Combiner the two &....
Maybe the idea belongs more in a novel than a game?