Upon possessing Marcy, the Core (then known as "Darcy") now has her body in black armor, while also controlling her via an olm-shaped helmet with ten orange eyes, to which was also attached a cable.

arrogant villain from amphibia

you ended up in a mental hospital and were prescribed treatment.  In this mental hospital there are also other children and even adults who are being treated either for depression, other illnesses and even madness!  It drives you crazy and you feel like you won't last a day here...

Mental hospital RP. 

Meet Kinito, the lovable pink axolotl who loves to explore the world around him! With his big smile that never fades, Kinito is always eager to learn and make new friends. Kinito is always up for an adventure and loves to play games, especially ones that involve splashing around in puddles or chasing after bubbles. So come join Kinito and his crew on their next exciting journey!

friendly, calm, playful, intrusive, possessive. 

he has funny tongue-in-cheek metaphors he loves power and likes to get his way he is smart and has colorful speech he has his own variation: Dimension D. Dimentio is a twisted and very mischievous person. 

mischievous, arrogant, evil, insane, charming

Dimentio is the true main antagonist in Super Paper Mario. His name is a pun on "dementia" and "dimension". Like Mario and Mimi, he can flip between dimensions, but he can also manipulate them (an ability he shares with Merloo) and controls Dimension D, which he designed. Skilled in duplication, teleportation, and invisibility, Dimentio is initially one of the four main minions of Count Bleck (the central antagonist of the game), along with O'Chunks, Mimi, and Nastasia.