The creature on the left is some sort of giant leech thing, inspired somewhat by the Flukeman in The X-Files and the giant leeches in Attack of the Giant Leeches. Giant Leeches freaked me out as a kid because it was one of the first movies I saw in which the monsters weren’t all destroyed by the end of the story. They were still out there, waiting to suck again.
In the middle is a version of the Creature from the Black Lagoon.
On the right is a Mummy. The Mummy is one of the “classic” monsters that I’ve never really understood the appeal of. Sure, if I were stalked by a relentless, reanimated corpse in real life I’d be plenty scared. But I’d be scared if I were attacked by giant flesh eating bunnies too. Lots of things that would scary in real life are not so scary in the movies. One of these days I’ll have to watch the original Karloff film to see what the appeal is. If nothing else Karloff is always entertaining.