One of the problems with using miniatures or props for monsters is that you can never have enough different ones to represent all of the multifarious possibilities that you'll ever need. The solution is to use things you have lying around the house.

We're pretty sure the Daleks started out this way, when Terry Nation was running a sci-fi game with Ray Cusick and a bunch of their friends, and grabbed a pair of salt and pepper shakers.

Transcript

{A montage of shots of various aliens inside the cantina, with the band playing music over the top}
Luke: Wow, I've never seen so many people, and... things.
C-3PO: The things are also people.
Luke: What, even that thing?
R2-D2: It's a sock pupp... well, actually it's just a sock.
GM: Use your imagination!!