Normally an NPC, but becomes attackble during a step in the quest Saving Soles. If not engaged, the Magolemus will then remain for fifteen minutes, and then despawn for two hours (unconfirmed).
A Projection of Najena spawns over its corpse immediately upon its death. All people on the quest Saving Soles should quickly hail her. The NPC does not despawn as a result of conversation options, but rather will despawn after roughly a 2-minute timer.
The largest concern is handling his knock-back. It is recommended that the nearby mobs be cleared and the tank quickly move the Magolemus near a rock or wall (without lava) so that the tank's back can rest against the wall. All other personnel should be behind the Magolemus the entire time.