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no. slaking had illusion, but this has happened before when no pokemon had illusion. btw, this is balancedhackmons.
also, if it was because of illusion, the stats would not have been copied
btw, how do i upload an image to a post?
Switching Pokemon Bug
this has happened to me several times. when switching pokemon, the pokemon that comes out takes the shape of a different poke in my party, but has the same moves and stats as the one i intended to switch in.