If it weren't for my other pets that I would prefer to stay uneaten, I would take Miffy. I honestly wonder where he came from, and what his life was like, etc. (see my other comment for interesting things I noticed about him). I'm curious as to where his hatred and violence came from - was he always evil? Maybe it was generations of being feared, hated, people trying to kill him.. he just decided to hate back, and use the fear to get what he wants, because he doesn't know how else to. This might be my love for cats speaking here, but maybe he isn't pure evil?

Perhaps a change of caretaking tactics might help - I'd try getting a food dispenser so he can get the perfect amount of food himself, even when you're not home. I wonder how he'd react to having a caretaker who did what he wanted, but wasn't scared of him - like, didn't run away from him, didn't react very much to being bit/scratched, etc. He uses fear to get what he wants - what if he wasn't treated like a feared/hated dictator, but just a very needy housecat or roommate? Like, "okay, okay, your royal miffy-ness. here's your food. now if you could let go of my arm that would be great." "miffy, that's my shirt - y'know what, keep it. i have others." "did you enjoy your daily kill? great. i'm not going near that damn room again, so you can leave all your animal carcasses there. oh, and theres a bunch of mice in the basement, would you mind getting rid of them? thanks." "shit, what the fu-! oh, it's just you crawling on the ceiling again. what the hell are you doing up there? and how do you even do that??" "okay, mr. sassypants, i get it. you're ferocious. good for you. you just gonna keep gnawing my leg, or..." I wonder if he'd become less violent if his caretaker was less afraid of him, but still gave him what he wanted.