From BZPB Wiki

Metrotitan is a robot roughly the size of a skyscraper. He appeared during the Battle of Mata Nui II, stepped on a skeleton, shot at the Baterra, and then fought Lonka and Parkin. He was then attacked by billions of ships User John Sheppard magically conjured up.

He re-appeared during the Battle of Mordor, and attacked Uterio di Armechio's troops. They then tied up his legs with cable, causing him to fall and crush someone called Jim White.