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 .
	+ Shoots 8 projectiles in all directions.

Independently of his projectile attack:

* 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.

## 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 and destroy 10 Tinted Rocks.

* 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  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 , waiting for  to activate before shooting Isaac, or placing multiple bombs and detonating them all at once with .  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*. 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.