Anomalous Object

Anomalous Object is the final component of the Magnum Opus quest, which ends with the Forerunner exotic sidearm. After opening a rock barrier with the Strange Key, Guardians follow a cave past a jumping puzzle to a cryo pod. Opening the pod yields the Anomalous Object, which is taken to Banshee-44 in the Tower; he repairs it into the finished sidearm.

A separate Season 12 legendary quest with the same name, offered by Failsafe on Nessus, is unrelated.