Cast is what you think it is with one exception. You have Bud Abbott and Lou Costello. They are their normal personas. Lon Chaney Jr. is the Wolf Man and Bela Lugosi is Dracula. Lugosi is apparently smacked out his mind by this point of his life. Frankenstein's Monster I always thought was Boris Karloff but it's some look-a-like named Glenn Strange. There are also a couple of chicks and a pretty boy, none of whom I recognize, that play central parts. Oh, and Vincent Price is sort in like 10-seconds of the movie. He's the uncredited voice of the Invisible Man.
Gist of the movie is that Abbott and Costello deliver wax monsters figures (Frankenstein's monster and Dracula) to a wax museum. However, the monsters come alive and take off. The Wolf Man is onto this shit though tries to warn these idiots. Costello sees the shit go down but can't convince Abbott. Also, Costello is trying to slay two chicks at the same time, I'm pretty sure. They are into him, but he's a moron. The fact that he is so dumb makes Dracula want to use his brain for Frankenstein monster's body so he can control it. Seems like something of a Get Out situation. It doesn't really hold up under scrutiny, but, again, fun.