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Looks like I got nothing for Megamom or Arceus.
Nidoking can take out Xerneas and probably Rayquza with Ice Beam (hopefully). If not, I'll leave Rayquza to Palkia.
Umbreon can handle Mewtwo with SwagPlay shenanigans (assuming this is on the cart).
I guess Tail Glow + Thunder can deal with Kyogre, but holy shit is that a stretch.