In Chapter 888 of One Piece, cute bunny girl Carrot reveals that Minks (the race of animal people that she's a part of) can transform into a more powerful "Sulong" (Chinese for "Moon Lion") form under the full moon. She becomes taller and more slender, her eyes turn blood red, and her hair and tail become much more long and flowing, with her hair turning white. It's not the most drastic transformation I've seen, but she looks different enough that I thought it was worth a mention.
Here's the best art I've seen to show the difference between her forms.
As for the anime, it's going to happen in episode 862, which airs on the 18th.
Here's a preview.