For gen 6 besides Slyveon, its Noivern. I just love the design. Oh also Tyrantrum. Its a T-Rex Pokemon, a T-Rex Pokemon.

a cartoon character with a heart shaped face is standing in a field

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Last gen because I haven't played past 7. I was just burnt out from open world games but I do want to play them. They look fun. For Sun and Moon, Mimikyu. Again Ghost type is my favorite but also the design idea is cool. I really like most of Gen 7's designs though.

a cartoon character with a purple tail and pink cheeks

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