It's All the World's Fault

The Protagonist Is an Experimental Subject, Tormented in a Lab, but Eventually Escapes

The Protagonist Merges with a Strange Creature and Undergoes Bizarre Changes

Novels Where the Protagonist Gradually Becomes Less and Less Human, or Less Like a Normal Creature

Looking for books like The Guest, Your Mom's Tentacles Are Crying! The stranger the better, like Dr. Apple in The Guest, Your Mom's Tentacles Are Crying! (either her battlefield form or her true form).

The Protagonist Becomes a Weapon, Spirit, Beast, Monster, or Machine and Evolves

The Male Lead Gets Infected and Controlled, Changing Until He's No Longer Human