Isaac (Boss)

This article is about the boss. For the character, see Isaac.

Isaac is the boss of the Cathedral, 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 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:

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 Cricket's Body.
- Shoots 8 projectiles in all directions.

Independently of his projectile attack:

Summons Angelic Babies in a pair.
- Directly below him.
Summons 2 Crack the Sky 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 Crack the Sky 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.

Gallery[]

Isaac in-game.
Isaac in his second phase.
Isaac in his third phase.
Isaac as one of Delirium's forms.

Unlockable Achievements[]

The Polaroid - Defeat Isaac 5 times.

BRAINS! - Defeat Isaac 5 times.

PONG - Defeat Isaac 5 times.

Something Icky - Defeat Isaac 10 times.

Isaac's Tears - Defeat Isaac as Isaac.

A Cross - Defeat Isaac as Magdalene.

A Bag of Pennies - Defeat Isaac as Cain.

PAY TO PLAY - Defeat Isaac as Cain.

Guillotine - Defeat Isaac as Judas.

The D6 - Defeat Isaac as ???.

Eve's Bird Foot - Defeat Isaac as Eve.

Bloody Lust - Defeat Isaac as Samson.

Satanic Bible - Defeat Isaac as Azazel.

Lazarus' Rags - Defeat Isaac as Lazarus.

Blank Card - Defeat Isaac as Eden.

Isaac's Heart - Defeat Isaac as The Lost.

Rune Bag - Defeat Isaac as Lilith.

Keeper holds Wooden Nickel - Defeat Isaac as Keeper.

Locust of Wrath - Defeat Isaac as Apollyon.

Slipped Rib - Defeat Isaac as The Forgotten.

Book of Virtues - Defeat Isaac as Bethany.

The Stairway - Defeat Isaac as Jacob and Esau.

Godhead - Earn all 5 / 9 (except Ultra Greed) / 10 / 12 Completion Marks on Hard mode as The Lost.

Mom's Lock - Defeat Isaac, ???, Satan, and The Lamb as Tainted Isaac.

Holy Crown - Defeat Isaac, ???, Satan, and The Lamb as Tainted Magdalene.

Gilded Key - Defeat Isaac, ???, Satan, and The Lamb as Tainted Cain.

Your Soul - Defeat Isaac, ???, Satan, and The Lamb as Tainted Judas.

Dingle Berry - Defeat Isaac, ???, Satan, and The Lamb as Tainted ???.

Strange Key - Defeat Isaac, ???, Satan, and The Lamb as Tainted Eve.

Temporary Tattoo - Defeat Isaac, ???, Satan, and The Lamb as Tainted Samson.

Wicked Crown - Defeat Isaac, ???, Satan, and The Lamb as Tainted Azazel.

Torn Pocket - Defeat Isaac, ???, Satan, and The Lamb as Tainted Lazarus.

Nuh Uh! - Defeat Isaac, ???, Satan, and The Lamb as Tainted Eden.

Kid's Drawing - Defeat Isaac, ???, Satan, and The Lamb as Tainted Lost.

The Twins - Defeat Isaac, ???, Satan, and The Lamb as Tainted Lilith.

Keeper's Bargain - Defeat Isaac, ???, Satan, and The Lamb as Tainted Keeper.

Cricket Leg - Defeat Isaac, ???, Satan, and The Lamb as Tainted Apollyon.

Polished Bone - Defeat Isaac, ???, Satan, and The Lamb as Tainted Forgotten.

Expansion Pack - Defeat Isaac, ???, Satan, and The Lamb as Tainted Bethany.

RC Remote - Defeat Isaac, ???, Satan, and The Lamb as Tainted Jacob.

Notes[]

Every time Isaac is defeated, the current savefile's image changes until The Polaroid is unlocked.
Isaac does not begin attacking until he has been damaged. This can be exploited to make the fight much easier by dealing large amounts of damage in the first hit. Methods of doing this include saving up a large amount of tears with Anti-Gravity, waiting for Kidney Stone to activate before shooting Isaac, or placing multiple bombs and detonating them all at once with Remote Detonator. Glass Cannon can also provide a high-damage initial shot, but doing this is extremely risky due to Glass Cannon's additional effect of reducing health to one half-heart.
- Glass Cannon no longer reduces health on use, so it can be used against Isaac much more effectively.

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.^[1] 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 ???.
Isaac and ???'s boss portraits were changed to match their appearances on the transition screen between levels. This was also the case in the original Flash game.
- Blighted Ovum, Big Horn, Triachnid, Isaac, and ??? are the only bosses whose portraits were completely changed in Repentance (beyond simply adding more detail). Of these, only Triachnid, Isaac, and ??? didn't receive new sprites.