Go to Kakaboom Island (when it is time) and follow Fluffy. She will lead you to a big Magmaquin. Fight it with the nearby turret. First it will throw rocks. Shoot them down. It should repeat this a few times, then it will turn around. Aim at its back and repeatedly press X to fire a strong beam. Repeat this until it is dead. You will then get a piece of the chassis. there Will be two more Magmaquin. Also kill them using the previous strategy to get the other two chassis pieces. Note: Only Shadow Stones can be used on it.