How do you kill this guy? He's a floating pyramid head enemy that seems to give all the other enemies in the room homing bullets... I killed everything else and the shield around him disappeared, but he was still invincible. Even tried bombs, no luck; had to bomb out of the room.

Is it because I had the horseman familiar from Glacier that spawns fly minions? I noticed that the purple triangle mark that appeared above some of the enemies during the fight started appearing above the fly minions...