The Fallen Light

The Fallen Light is a Boss that can be found in Ivory Palace. It is the new final boss added by The Ascent of Isaac Godmode and grants the new ending when defeated.

Behavior

The Fallen Light is always fought in a 2×2 room slightly reduced by the walls of pillars and the chasm bordering the room.

Due to the slow nature of some of the projectiles and the increasingly shorter cooldown between each attack as its HP goes down, The Fallen Light tends to overlap its attacks a lot.

Phase 1

The Fallen Light will randomly choose between the following attacks:

Shoots a ring of red bone projectiles in a circular shape around it, waving to form a star shape, allowing Isaac to walk through the gap between the bones.
Shoots two big rings of blood shots in all directions, the second wave being slightly slower than the first one.
Fires 3 waves of 10 telegraphed Revelation beams in all directions with varying angles.
Shoots a wave of skulls projectiles regularly stopping and moving while summoning Crack the Sky beams at the border of the screen, slowly approaching The Fallen Light while moving in a spiral pattern.
4 moving shadows appear on the floor. After a short while, giant bones fall from the ceiling at those locations, spawning some short rock waves. Those bones explode into giant puddles of damaging red creep after some seconds.

Phase 2

After The Fallen Light has its HP reduced to 75%, it bleeds and the walls start to crack, revealing blood inside, signaling the start of the second phase. The Fallen Light adds the following attack:

Shoots a ring of wiggling bone projectiles that alternate between rotating clockwise and counterclockwise as they move outwards.

Its previous attacks also behave differently:

The blood shots rings attack adds homing blood shots to the mix.
The Crack the Sky beams approach Isaac instead of the Fallen Light, forcing Isaac to slowly move inside the circle they form to avoid being hit. The skull projectiles are denser for this phase.
The Revelation Beams attack now has 12 beams per wave.
The bone star pattern loses points and is slightly faster.
6 bones fall from the ceiling instead of 4.

Phase 3

After The Fallen Light's HP is reduced to 50%, it bleeds and the walls crack even more, signaling the start of the third phase. The Fallen Light adds the following attacks:

Shoots two big blood shots, one towards Isaac and one on the opposite direction, which shoots blood shots perpendicular of itself.
Regularly bleeds a bunch of blood shots around it.

Its previous attacks also behave differently:

There are no more homing shots in the wave of blood projectiles. However, there are more blood shots added to create a larger overlap between the attacks.
The Crack the Sky beams approach Isaac much closer than in phase 2, forcing Isaac to slowly move inside the circle they form to avoid being hit. The skull projectiles are extremely dense for this phase.
The Revelation Beams attack has 14 beams per wave, and is now predictive of the player's movement for determining the angle to use.
The bone star pattern loses points and is slightly faster.
The ring of wiggling bone projectiles is denser.
8 bones fall from the ceiling instead of 6.

After The Fallen Light's health approaches 10% remaining, it becomes invulnerable, moving to the center of a room. Once there, a big hole appears below it, revealing a giant hand dragging the boss down to the unknown depths below. If Isaac doesn't have the Vessel of Purity or one of its cracked forms, the fight ends and the typical ending Giant Chest spawns, unlocking the corresponding character unlocks.

Secret Final Phase

The Sign is the secret final phase of The Fallen Light boss fight.

How to access

The Sign only appears if Isaac has the Vessel of Purity or one of its cracked forms upon defeating The Fallen Light. To get the Vessel of Purity, Isaac needs to find a Masked Statue in the Ivory Palace's Secret Room. Isaac then needs to bomb the statue 3 times, each time spawning a wave of enemies to defeat. When the 3 waves have been defeated, an angel baby akin to Late Delivery appears to spawn the Vessel of Purity. After that comes the hardest part, which is to reach and defeat The Fallen Light, taking less than 3 hits along the way or else the Vessel of Purity is destroyed, locking the player from seeing the secret final phase. If Isaac succeeds, after being dragged in the hole, The Fallen Light's head resurfaces and reveals The Sign, destroying the head and starting the fight.

Behavior

This fight is very unusual as the Sign has an armor value of 500, meaning all DPS is minimized to a large degree. However, the Sign will be draining its own health over time, which takes around 2 minutes to reach 0. If you are constantly attacking The Sign, the time of the fight can be cut roughly in half, depending on your DPS. Once the Sign reaches 10% or lower health, however, it cannot take any more damage from the player. During the entire fight, if Isaac doesn't move, a charge bar appears near The Sign. When filled, a Crack the Sky beam appears on top of Isaac. The Sign will execute its attacks in the following order:

Summons rings of blood shots, with a hole randomly placed on each ring, from outside of the room, closing by The Sign.
- You can somewhat easily avoid this attack if you have low speed by being very close to the border of the rooms and navigate between the projectiles.
Summons 10 blood shots approaching The Sign before exploding into 4 smaller blood shots.
- This attack is easily avoided by staying close to The Sign.
Summons waves of 6 big blood shots that alternate between rotating clockwise and counterclockwise as they move towards, then outwards The Sign.
- Stay close to the walls and watch out for the coming projectiles from outside the screen.
The two previous attacks, mixed together. There are fewer big blood shots, however.
Finally, a weaker version of all three attack patterns is used at once.

Once that final attack is finished, The Sign emits a bright light before disappearing and the fight ends. The typical ending Giant Chest spawns and an item is unlocked if the player doesn't have the character achievement already. However for your effort defeating this secret final phase, The Sign character will be unlocked, if not unlocked already, or if unlocked will get buffed. The first 5 times you manage to defeat this secret final phase after unlocking The Sign, the character gets stronger.

In the event that you successfully make it to The Sign but end up dying, you will still receive the character unlock for defeating the Fallen Light, but you will not buff The Sign like you would had you defeated the secret phase as well.