The Lamb

Then I saw a Lamb, looking as if it had been slain, standing at the center of the throne, encircled by the four living creatures and the elders...

The Lamb had seven horns and seven eyes, which are the seven spirits of God sent out into all the earth. [...]

Then I heard every creature in heaven and on earth and under the earth and on the sea, and all that is in them, saying: “To him who sits on the throne and to the Lamb be praise and honor and glory and power, for ever and ever!” [...]

I watched as the Lamb opened the sixth seal. There was a great earthquake. The sun turned black like sackcloth made of goat hair, the whole moon turned blood red, and the stars in the sky fell to earth, as figs drop from a fig tree when shaken by a strong wind. The heavens receded like a scroll being rolled up, and every mountain and island was removed from its place.

Then the kings of the earth, the princes, the generals, the rich, the mighty, and everyone else, both slave and free, hid in caves and among the rocks of the mountains. They called to the mountains and the rocks, “Fall on us and hide us from the face of him who sits on the throne and from the wrath of the Lamb! For the great day of their wrath has come, and who can withstand it?”

—Revelation 5:6, 5:13, and 6:12-17

Template:BossTable The Lamb is the final boss of the Dark Room.

Behavior

The Lamb is a two-part fight. The first phase transitions into the second phase when the boss reaches 50% health.

Phase 1

The Lamb has a variety of attacks in this phase:

Fires a 2-to-4-way shot directly at the player.
Unleashes a scatter shot of many small explosive tears in a random fashion.
Fires a constant stream of non-explosive shots in a circular pattern around itself, like Mom's Heart/It Lives.
Shoots a semi-circular pattern around itself consisting of smaller, non-explosive shots that will split apart once they make contact with any surface, like The Parasite.
Fires up to five lines of non-explosive shots. Spawns attack flies during this attack.
Fires a 3-way or a V shot that will consist of homing tears towards Isaac. Spawns attack flies during this attack.

Phase 2

Once The Lamb reaches 50% health, it will fall to the ground and its head will detach from the body. This phase has each part of The Lamb attacking independently of each other; the head gains three attacks in addition to the attacks from Phase 1, while the body only has two attacks that it will use at random intervals.

The Head's Attacks

The head of the Lamb can use any of the attacks from Phase 1, but now has three additional attacks. It operates independently of the body and does not seem to change its behavior at all when the body is defeated.

Charges extremely quickly directly towards the player, stopping at the edge of the room.
Stops in place and fires four Brimstone beams in the cardinal directions. The beams may rotate either clockwise or counterclockwise.
Fires a large burst of homing tears at the player, similar to the combination of Monstro's Lung and Spoon Bender.
The head will start moving again after each attack is finished.

The Body's Attacks

The body of the Lamb is stationary and will remain wherever the Lamb was at the end of Phase 1. It does not have any of Phase 1's attacks. The body will use its attacks at random intervals and does not seem to react to anything, though it will not attack while the head is attacking. It will attack in the same way regardless of whether or not the head is still alive, and does not seem to attack any more often even if the player stands in its line of fire.

Fires a large burst of tears at the player similar to a Monstro's Lung attack. They may look like explosive or homing tears, but they have no special effects whatsoever.
Spawns up to 5 attack flies.
- If the head is defeated first, the body will be able to spawn up to 25 attack flies.
When the body is killed, a Curse of Darkness effect will cover the entire floor for a significantly longer period of time than the effect other bosses create.

Gallery

The Lamb in-game.
The Lamb in his second phase.
The Lamb as one of Delirium's forms.
The Lamb intro.png

Vs. screen intro.
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First attack (Vita).
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Second attack (Vita).
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Head: Charging attack (Vita).
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Head: Monstro-like attack (Vita).
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Head: Brimstone attack (Vita).
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Head: Brimstone-like attack (Vita).
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Body: Fly Spawning (Vita).
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Body: Burst attack (Vita).
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The Lamb when defeated (Vita).

Unlockable Items

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In addition, beating the Lamb with a particular character will unlock the Negative Completion Mark for that character.

Notes

The Lamb can be reached before The Negative is unlocked if a Sacrifice Room is used 12 or more times.

Trivia

The music that plays during this battle is titled The Fallen Angel.^[1]
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.
Jesus Christ is often referred to as "the Lamb" in the Bible, therefore it is possible that this boss represents Christ in some darker sense. ^[2]
One of the Fortune Teller's fortunes states "Your soul is hidden deep within the darkness". This may be a reference to the Lost's unlockable item for defeating the Lamb, which is The Soul. The Soul could be considered "hidden deep within the darkness" because The Lamb is the boss of the Dark Room, and you have to beat it with the hidden character in order to unlock it.
The Vs. Screen introduction depicts the Lamb with solid black bones, but in-game the Lamb actually has pure white bones.
The Lamb shares his 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.

References

Bugs

Bug!	If The Lamb is shooting projectiles and you damage it over half of its health, it will continue to fire until dead or it has finished its attack.

Bug!	Killing the body in around 5 seconds will make the body stand inside of the chest, making you unable to reach it (and end the game). You can fix this by going in and out of the room.