An explanation of the strategy for the Archangel Headraniel boss fight.
Headraniel will throw skulls at you. Don't stand too close to the bottom edge of the room, because you need the skulls to land on the platform, instead of being destroyed by being thrown at the wall. Pick up a skull and throw it at Headraniel to knock off a part of his body. Pick up the statue parts and throw them at Headraniel. If you wait too long, he will float to the platform and retrieve his body parts. Sometimes he will spin a fan that pulls you toward the pit. After he has no body parts left to throw, his eyes will glow and he will throw himself at you. Pick him up and throw him into the pit.
If Headraniel is the boss of the fourth dungeon or later, there will be a second phase of the battle. In the second phase, he will make a circle of skulls appear around himself, then will throw the skulls at you one-by-one, then after the skulls are gone, will make flames shoot out on the platform where you are standing, so be sure to move to dodge this.