https://en.wikipedia.org/wiki/Rat_king
"for it is said they can summon an army of rats from the shadows."
put in a motherfucking rat themed dungeon with this guy as the boss. with their nervous systems connected at the tail these fuckers are smarter than the average rat. and dont forget the shadow rat summoning ability. you face an infinite number of rats until you take this fucker down.
i dont have any idea as to what the specific rewards could be, would you guys mind suggesting some down below?