You'd have to pick something with a strong type combination. Something with no weaknesses, or just one. And you'd wanna be able to teach them a lot of different typed moves, too. A good ability like Volt Absorb or something else that makes them immune to certain typed moves would be good, too.

[ She's obviously done some thinking. ]

In the games it was pretty easy, 'cause you just ended up way overleveled. I think it's more complicated here.