I'm going with Mewtwo. Reason being, it's got trouble stopping the first set. It's basically forced to run Power Swap/Toxic/Protect/Rest, which is... probably even worse than the Manaphy set, since at least Swagger messes with everything. It could drop Protect for Fire Blast and kind of hurt itself in the process, which makes it kind of able to break steels, but seeing as it needs a lot of defense as well, it's still walled and stomped by plenty. Meanwhile, it's still semi-setup bait, since you can still boost on it after it steals your boosts-it'll just take longer. (If it drops power swap for anything, the enemy Mewtwo can theoretically boost like crazy and stomp it hard.)