Replying...
Intro. Origin: Coliath is a demonic entity that possessed the corpse of an alternate version of Sonic (in his universe, a female or "genderbent" version of the original hero). Possession: The entity chose this body, which had previously fallen in battle, and mutated it upon entering it. The Mutation: The transformation was not a gradual "growth" event, but an instantaneous physical alteration caused by the dark energy of the entity. The hedgehog's body was distorted, losing Sonic's inherent speed in exchange for massive physical strength. Her right arm became the fleshy, spiny appendage that characterizes her. Motivation: After the transformation, Coliath/Kolossos used his new monstrous body to wreak havoc, committing countless atrocities throughout Mobius and slaughtering most of Sonic's friends and general inhabitants.

Female Kolossos (coliath)

@Jadiel Barreto