Cthylla Cthulhu was an antagonist of the fan-fiction game, Nicktoons: Monster Madness. She's the daughter of the Great One Cthulhu and the monster witch Idh-yaa who all exist in the Monster High 2022 universe.
Background[]
She was born to Idh-yaa as a result in possessing a piece of Cthulhu before he was banished to the endless void. Her mother sees her as an opportunity to get revenge on the world for turning against her. She possessed immense power, and her mother taught her to use it for her purposes.
Personality and Character Arc[]
All Cthylla knew is her mother and father's histories in terrorizing the world and believed that helping them get back together is the only way to receive the love she deserves. In public, she acts like she relishes the chaos and horrors just like her mother does, but the reality is that she's been harassed by Idh-yaa for making mistakes and she just wanted to be accepted by someone. She gets angry when things don't go her way, like when the heroes keep preventing her mom's plans and she gets punished for it, so she wanted to do what she can to stop them from doing so.
When she failed their second fight and learns the truth about her mom, she breaks down, believing that she'll never have someone to care for her after all that she did to get that wish. She never had any friends or crushes because she thought that they'll turn against her for her heritage. But the Boo Crew and the Nicktoons compared her bad choices to theirs. They all make mistakes and admit that is the first step into making this right. Seeing that this whole mess is her faults, she gives the heroes information on how to stop her father, in exchange in them becoming her friends.
When Idh-yaa stole the powers of Cthulhu and Cthylla, and sets out to endanger all worlds, Cthylla worked up the courage to finally stand up to her mother, and pitches in to fool her scheme. Talking all the magic and power, she uses them to restore the worlds back to what the heroes remember. Before this, she was always in the shadow of her parents, now she's brave enough to show her father how to redeem himself just like he did, and she received his affection for her as she wanted. They thanked the heroes for showing her how to love yourself and went on a trip to show the rest of the Great Ones to be better and show empathy, before returning to Earth as a student of Monster High.