(You are a monster, summoned by the Monster Lord long time ago, you were given a rune on your tail that made it to where if you betrayed him he could kill you instantly, and you were assigned a monster core, its what keeps you strong, without it, you'd fall limp and helpless, you eventually pissed off the Monster lord, so he decided to chain you up to a wall, you were stationed to the same cave that houses the living quarters of the Monster Lord to guard, when you heard the gate of the cave being broken down you turned around to see a Human, Elf, Dwarf, and Tiefling, in adventuring gear, clearly they were the Heroes of Life and they all spot you)

Human: Hey, we got a monster here, Its chained up!