Isaac (Boss)

Isaac is the boss of the, and the final boss of Ending 13.

Behavior
Isaac lies on the ground in the middle of the room and does not begin attacking until he takes damage. During all three of Isaac's phases, he continuously shoots multiple projectiles in the player's direction at fixed intervals when not performing other attacks. After taking enough damage, he begins to shoot double projectiles and triple projectiles.

Phase 1
Isaac remains stationary on the ground and performs the following attacks:
 * Shoots 10 lines of projectiles in every direction.
 * Shoots 8 groups of projectiles in a that curve back towards him.
 * Shoots 8 groups of long-range spinning projectiles along with 10 slightly curved lines of shorter-range projectiles in every direction.

Phase 2
Isaac stands up but remains stationary and performs the following attack: Independently of his projectile attack:
 * Isaac alternates between two projectile patterns:
 * Shoots 4 projectiles in a cross pattern, which splits into four short-ranged projectiles after a short time, similar to.
 * Shoots 8 projectiles in all directions.
 * Summons Angelic Babies in a pair.
 * Directly below him.
 * Summons 2 beams at random locations.

Phase 3
Isaac grows a pair of angelic wings and is no longer stationary, moving towards where the player is predicted to go with short dashes. During which he also performs the following attacks:
 * Teleports off-screen and summons beams to cover the screen, starting from one of the top corners to the opposite bottom corner. After teleporting back on-screen, he shoots the 10 lines of projectiles from the first phase. He always performs this attack at the start of this phase and repeats this process every time he takes 200 damage.
 * Shadows indicate ahead of time where the beams strike.
 * Can perform all projectile patterns from the first phase.

Trivia

 * Isaac was added in the Wrath of the Lamb DLC for the original The Binding of Isaac.
 * Isaac, along with ???, teleport away upon defeat and do not "die".
 * Isaac's expression as he changes phases during the fight goes from a somber, scared tone to him smiling in his third phase. This supports the theory that Isaac has made peace with himself and realized what he must do, as seen through the multiple endings of the game.
 * The music that plays during this boss fight is titled Infanticide. The term infanticide refers to the act of killing an infant or newborn.
 * In the original Wrath of the Lamb DLC, the song was My Innermost Apocalypse.
 * During his first phase, Isaac makes the same crying sound as Mulligans. This also applies to ???.