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Mew
Pink core. If you played any UU during xy, you'll remember that unbreakable core that was frustrating as hell to play against (it was half of the reason why I used Hydra on most of my teams)
Mew. (Even though I nominated entei, I don't think it's as deserving as the pink clone. It'd be on my ideal list but the community one voted in a couple things I disagree with.)