The Lamb

The Lamb is the boss of the, and the final boss of Ending 15.

Phase 1
The Lamb floats towards Isaac and performs the following attacks:
 * Fires 2-4 lines of homing projectiles in a spread that rotate to follow Isaac's movements.
 * Unleashes a burst of many small -like projectiles in random directions.
 * Fires 6 rings of 10 projectiles outwards with one projectile always aimed in Isaac's direction. The Lamb continues to move towards Isaac but at a very slow pace while performing this attack.
 * Shoots rotating waves of 3 projectiles in a around itself in all directions that split apart once they make contact with any surface, similar to.
 * Fires 5 rotating lines of projectiles.
 * The Lamb occasionally spawns 0-3 Attack Flies during any of the 4 attacks above.

Phase 2
Once The Lamb reaches 50% HP, its body detaches from its head and falls to the ground. This phase has each part of The Lamb attacking independently of each other.

The head of The Lamb continues to chase Isaac and can still perform most of the attacks from Phase 1. It loses the explosive shot attack and no longer spawns Attack Flies but gains 3 additional attacks:
 * Charges extremely quickly directly towards Isaac, stopping at the edge of the room.
 * Stops in place and fires four beams in the cardinal directions. The beams can rotate 90 degrees either clockwise or counterclockwise.
 * Fires a large burst of homing projectiles towards Isaac, similar to the combination of and.
 * Defeating the body first has no effect on the head's behavior.

The body of the Lamb remains stationary at the position the Lamb was at the end of Phase 1. The body has one attack which it performs at random intervals but while the head is attacking:
 * Fires a large burst of disorganized projectiles in all directions and spawns up to 5 Attack Flies.
 * If the head is defeated first, the body can spawn up to 25 Attack Flies.
 * When the body is killed, a Curse of Darkness effect is applied for a long period of time.

Trivia

 * Despite Jesus Christ often being referred to as the "Lamb of God" in the Bible in the books of John and Revelation, The Lamb in this scenario most likely refers instead to the lamb that was sacrificed in Isaac's place in the story of Abraham and Isaac which this game is based upon.
 * The music that plays during this battle is titled The Fallen Angel.
 * The Lamb is likely a reference to the name of the original Binding of Isaac's DLC expansion, "the Wrath of the Lamb". Due to the absence of any mention of a Lamb in the original game, this may be the character eponymous with The Wrath of the Lamb expansion pack.
 * The Lamb's battle portrait depicts it with dark grey bones, but in-game the Lamb has white bones.
 * The Lamb shares its name with a level from Edmund's previous game Super Meat Boy.
 * The Lamb is one of the three bosses that can dim the room (making a temporary Curse of Darkness effect). The other bosses are Dark One and The Adversary.
 * During an AMA stream, Edmund McMillen confirmed that The Lamb is "Isaac, dead, as a demon," and that it represents "his evil side." [2 ]

Bugs
The Lamb ‎