Although Luz was born human, she later becomes capable of transforming into some black-scaled, winged, reptilian creature with black eyes containing glowing blue irises. Eventually, it's revealed that she's become infused with magic and has evolved into a cambion, just like Emperor Belos. However, Chapter 106 discredits this with the strong implications that she's actually a Titan.
Katya, a witch in canon, is a witch who was turned into a vampire by her adoptive father here.
Several characters are turned into Fae, such as the Ambiguously HumanCoachman or the Mewman, Ms. Heinous/Meteora Butterfly. After being hinted near the end of Book 1, Chapter 66 reveals Amity to now be part Fae herself due to her deal with Puck to keep moving forward through hardship. The same chapter also reveals the Collector is a Fae, too.
Chapter 47 reveals that Skara, while still a witch, is also a werewolf, a trait which she inherited from her father, Slasher, with their ancestors first being infected during the Savage Ages.
Chapter 75 shows that Jackie Lynn Thomas, who was merely human in Star Vs. the Forces of Evil, is now half human, half mermaid.
Downplayed for Cat, as the sidetrack "Cat's Jubilee" shows that she has human ancestry in her family tree.
Bria, minor as she is, wasn't shown to be anything other than a normal witch. Here, she gets mutated into a chimera-like being thanks to Sonya experimenting on her.
Willow was originally just an incredibly powerful prodigy in plant magic. Here, she's a demigoddess whose power was gifted to her by Samshin Halmang, the Korean Goddess of Life.
