Dress you guinea pig up like Frankenstein!  We also have Frankenstein's Groom if you want a nice matching set!

Also, you could use it without the headpiece for an interesting suite jacket!

This costume's jacket is in velvetty green with purple collar and 3 patches on the jacket.  This jacket is attached with two hook and loop strips.  It runs big, so might not be good for tiny guinea pigs. If you fit other Thrills and Chills costumes, you should be fine. But the hook and loop closure will also help make some adjusting for size.