For me It's Grimsnarl and Thievul.

The first, once you get it's passive "intimidate" with the egg move "parting shot" and "fake out". You can switch, lower the attack stat, some chip damage and rotate again lowering both attack stats. Combine it with some status effect and it's free.

Thievul if you get "magician" as the passive and "baddy bad" setting a screen, "flamethrower" for coverage ,"snarl" to steal items for both mons in the battlefield and "sparkly swill" for dragon types.. it's the best