My girl- One of my Favorites ocs-
There is her Design-
Yes, the tail is inspired by Bondrewd from Made in Abyss- (who was also an Inspiration for this character-)

Little description :
she is a 12 years old demon/Cyborg/Reptile who have a eternal disease for divin punishment, who is dangerous and crazy but also very polite and smart. She is also the overload of the knowledge (manipulation) , a kind of scientist-witch and the CEO of « Bacteroid corporation » . Yes, that's make a lot of function for a 12 year old girl-
In case, no, she is not really a Mary Sue, she have a lot of flaws, also weaknesses and can't do all she want by herself because of her punishment, plus, she have some malus with her robotic body and powers.