Now I know there is only one Power Pony episode, but I was wondering if either in the comics or some other resource there was another canon villain?

6329990
Yes.

6329990
yes, the other Power Ponies villains are:

Mane-Iac:

Pharoah Phetlock

Long-Face:

Smudge:

High Heel:

and Finally Shadowmane:

6329997
6330009 Did that comic by any chance give Mane-iac's reason for wanting to destroy Maretropolis?

6330030
the only reason the Mane-iac gives is, that she and the other villains have been defeated by the Power Ponies, time and time again, which why Mane-iac suggests that the villains join forces.

6330030
Who says she wants to destroy Maretropolis?

6330097 Shementions it in the episode quite a few times.

6330285
Well, she does say she plans to destroy the city, but her plan is just to make everypony's manes go wild, so uh...
Eh, it's not like anything else in the episode made any sense.