That's odd, I have head of this happening to gengar only once before. Do you use Gecko or Riivo? and did you use the codes included?

The download didn't come with any codes, so you must be referring to the "Wario has no entry data," correct?
Well, I'm going to go try that and see if it works.

EDIT: I must be stupid because that code made it work perfectly fine.

Gengar seems to be glitchy for me.
Whenever I start a match with Gengar, the game freezes.

EDIT: The game also freezes when Gyarados attempts to climb a ladder.