Brain: So, Sin isn't scary enough...his appearance isn't scary enough...what if he turned into a monster? Or like something like that 

 Me: A small price to pay to make my brain happy

I have no idea why I wanted this, I made it where their jaw can unhinge and engulf a person's head and can crush a person's head  

Brain also wanted it where Sin accidentally gave Jeremy half of whatever this beast is...I also made a concept Au so yeah