Princess Peach

Princess Peach is the princess of Mushroom Kingdom, and owns Princess Peach's Castle, and is often kidnapped by Bowser. They appear after beating Bowser in the Sky in the end cutscene. However, in certain personalized copies, they can be unlocked as a playable character, usually after finding Delicious Cake and collecting it's star.

Skin Peach Corruption
In certain personalized copies, all textures on Princess Peach can turn into her skin color. It oddly usually happens after all red coin stars are collected.

PEACH120.Dream
A textureless peach model that can chase the player in Bowser in the Sky by floating towards them. However, they do not do anything when approaching Mario.

Braphog Transformation
If Princess Peach is used to play Bowser's Brap Barn, they unlock the ability to turn into a Big Braphog and use a form of the fart gas as an attack. Princess Peach is also immune to the fart gas in both forms, which fits with the theory that Peach created some of the farts in Bowser's Brap Barn.

Unused Legs
Found in the files of Super Mario 64 is an early Peach model with legs. However, it is believed they were removed when they could be seen when Peach first appears in the end cutscene through her dress.