This is the page that contains all the deleted information from Kingdom Hearts III
1) A lot of Maleficent's backstory was removed. Kingdom Hearts III did, originally, have a lot of information on Maleficent's back story, who she was before she became evil and how she felt at being excluded from Aurora's christening. Instead, a world featuring a younger version of her - showing her recorruption by the Darkness after her plan to kill Aurora failed - appears instead.
The parents of Sora and Riku and Kairi's adopted parents were supposed to appear.
Like the parents of Sora and Riku and the adopted parents of Kairi, Destiny Islands was supposed to appear, but was removed.