Well, look at it.
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The real Hatterene is the little white girl inside her "body" of hair. Could you walk if you had no feet or legs touching the ground? :P
It's previous evolutions, Hatenna
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and Hattrem
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Have legs and/or pigtails that function like legs. They can walk and run a lot better than Hatterene can.
And, as always, Gamefreak Logic.