All the monsters--Y.
Like "x", "y" is a lonely letter, with only 2 monsters. Soon I'll have to actually think before writing blog entries again.
On the other hand, all Y monsters are all good. Not even "D" can say that.
The proper image, if you can find a way to evoke it in the players, is the wampa--not the toy with the hugging arms but the way it looked and seemed on the screen when you were a kid--when Luke first wakes up--long-haired like an Afghan hound, bent over, devil-horned, but human enough that the word "cannibalistic" still seems to apply. Until he Forced that lightsaber into his hand, that was a horror movie--maybe the first one most of us ever saw.
Like a mummy, the monster has to be detached from it's cartoony associations (and various cartoony names) in order to imagine how frightening and believable a goatmanbeardevil hidden in an ice cave really is if you're trapped alone in a landmarkless wilderness.
These snake men work, how could they not? Snake-anythings work.
I don't like the South American/South East Asian associations of the name, as it suggests--in a D&D context--that they come from far away. I prefer the idea--like in Conan--that they come from the same place, but an earlier time. In my campaign, they're called Librarians--for reasons I'll explain in some post in the future.