Unlike most of the other Totem Pokemon, Totem Mimikyu somehow wasn't the most difficult of battles the second time around. If you are still having troubles with it, Ghost Types and Steel Types are your best bet at defeating it, specifically those that use Special Type Attacks. This is because Mimikyu will have all of its stats increased as the battle begins, as well as because Banette, one of the Pokemon it will call upon for help, will try using Will-o-wisp again your Pokemon.
Trevenant is also a great option against Totem Mimikyu, specially the one you can trade for in the Tapu Village Pokemon Center. Not only does this Trevenant know the move Will-o-wisp to cut Mimikyu's Attack in half, but it also knows moves like Leech Seed and Feint Attack to slowly crush this creepy Ghost Type Pokemon. Even if you don't lead with it, Trevenant could come quite in handy.