One of my favorite Mons to use is Azumarill. I've got one named Mercy. She takes people's souls. I recently got a Belly Drum set but I've yet to use it. The big issue is that you have to force a switch and have already weakened their switch-in for the set to work. Things like Raikou destroy Azu, and most people don't like their Azu checks being killed off so they play smart. :/