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Dk is NOT the biggest nerf, he's overall improved.
Link has NOT been overall nerfed, the only thing legitimately nerfed is his upB, as not its only situational (has much better recovery, but so does everyone else). I dont think he walks faster but alot of moves come out faster. He has larger hitboxes because his sword's range has been increased. All his non UP-B attacks are leagues better than their older form. His arials are weaker, I guess this is a nerf, but remember that they come out faster. Anyone who says Link is nerfed does not know how to play Link...
Biggest Nerf: Sheik, went from high tier, to lucky if shes better than Zelda. Spacies hit hard to but not as hard.
Biggest Buff: Can't decide between Zelda and Bowser, both very useful now and practically useless before. A Zelda main, I'm biased towards Zelda, but I think Bowser was worse than Zelda in melee and now is about the same level as her (much better than in melee), so mabye he got an overall bigger buff.
EDIT: G&W was worse than Zelda in melee (bottom tier) didn't know that. Yes there are a lot of holes in Zelda's game but she HAD ONLY HOLES IN MELEE, other than her kicks.
oh and btw her fair/uair arn't her only kill moves, though she does require more demanding spacing than most characters, remember that her kicks are much stronger than in melee to compensate, making them the same in melee (which was good). Her uair was not very good at ALL in melee, slow and not much kick, now its faster and has a lot more kick.
You're comparing to other characters, compare her to her useless melee self when your describing buffs and nerfs. Moving on to her nonkick moves, all of them got major buffs, as almost all of them were near useless in melee, they are now useful!