[@VATROU] I need a foil who isn't already one of my own characters. Because y'all don't want Might's ACTUAL foil. Because he's an asshole. Among my cruelest, most intelligent, and most powerful characters.

Because he's Might. But better, and evil.

Edit: 
Long Story Short: 
Might is equally as physically strong, fast, durable, and energetic as the person he's fighting. Allowing him to fight anyone on equal ground, unless they have no actual physical abilities and is exclusively something other than that. 

Doppler steals HALF (not all) the appearance of the person his skin has most recently touched, as well as any notable abilities and skills that they have. He also keeps an echo of the appearance of the person he touched before, making him fall into the uncanny valley.

Might is a Persona created by a man who lost his identity.

Doppler is a man who never had his own identity.