all you need is a mon with knock off, a mon with toxic, and a Toxapex
Start with the Knock off Pokemon. It doesn’t matter in they faint, as long as they get rid of the berry and Disguise. I suggest getting as much damage off with the knock off/toxic mon as you can so you get a safe switch into Toxapex. Venoshock will be STAB, super effective, poison boosted, and always crit because of Merciless. It should beat the Mimikyu pretty easily.
Just ignore the ally and if needed, bring another Toxapex if you have it. One should be enough, but unlucky crits do happen.
