Mega Satan

Mega Satan is a boss that appears in Chapter 6, and is the final boss of Ending 16.

Unlock
Mega Satan is located behind the Golden Gate at the starting room of and the. To unlock Mega Satan, the following criteria must be fulfilled:


 * ??? or The Lamb must have been defeated in an earlier run for the Golden Gate to spawn. Once that is done, the achievement "The Angels Await" will appear.


 * Reaching the to fight The Lamb or Mega Satan without having unlocked  can be achieved by either:
 * Taking the trapdoor in a Black Market from if one shows up.
 * Using Sacrifice Room 12 or more times.


 * Once unlocked, the Golden Gate can be opened using one of the following methods:
 * Defeating Uriel and Gabriel to obtain and . Collecting both pieces turns them into the Golden Key, which automatically opens the Golden Gate upon entering Chapter 6.
 * The Angels can be summoned by bombing an Angel Statue.
 * Sacrifice Rooms summons Uriel and Gabriel after stepping on the spikes for the 9th and 11th time, respectively.
 * Using in the starting room.
 * Using a in the starting room.
 * Instructing to unlock the door.
 * Using on the door.
 * Using a in the starting room.
 * Activating in the starting room.

Behavior
Passing through the Golden Gate and stepping onto the pentagram initiates the Mega Satan fight.

Phase 1
Mega Satan is accompanied by two hands, which serve as a barrier to protect him and an avenue for him to attack. His hands spread apart if Isaac gets close to him, and move together if Isaac moves away from him. Each hand has 600 HP, and destroying a hand deals 100 damage to Mega Satan. Each hand respawns 30 seconds after it’s destroyed.

Mega Satan has the following attacks:
 * Closes his eyes and then fires one of several projectile patterns, including:
 * 3-5 lines of blood projectiles. The angle these shots are fired at alternates between rotating clockwise and counterclockwise. The less lines of projectiles there are, the faster they travel and rotate.
 * Spreads of brown projectiles that split into 4 smaller projectiles after traveling far enough, similarly to.
 * 2 spirals of blood projectiles that very rapidly rotate clockwise, creating semi-circular waves of projectiles.
 * Rings of blood projectiles, fired in rapid bursts of 3.
 * 2 spirals of blood projectiles that rotate clockwise at different speeds.
 * 3 lines of blood projectiles that alternate between slowly curving right and left with every shot fired. The angle these lines of projectiles are fired out at alternates between slightly rotating clockwise and counterclockwise.
 * Closes his eyes and then fires a laser straight down. His hands always fully spread apart while charging the laser, regardless of Isaac's position.
 * Slams his head into the platforms 1-3 times, creating chaotic bursts of projectiles in all directions.
 * Holds up one hand, then slams it at Isaac, creating a circular rock wave on impact. This attack can’t be used if both hands are currently destroyed.
 * Slams both hands 3 times, alternating back and forth, creating rock waves that move towards the bottom of the screen. This attack can’t be used if either hand is currently destroyed.
 * Destroying a hand during this attack prevents it from creating more rock waves.
 * Mega Satan also spawns sets of mini-bosses to attack Isaac alongside him. These sets can be:
 * Gluttony and Envy
 * Sloth and Pride
 * Wrath and Greed
 * Lust
 * The Hollow
 * These mini-bosses can be damaged by Mega Satan’s attacks. His laser deals 36 damage per tick, while all others deal 10 damage per hit.
 * After taking enough damage, Mega Satan and his hands withdraw into the darkness behind him and become invulnerable. During this time, he spawns a wave of bosses or mini-bosses, which must be killed in order to make Mega Satan vulnerable again. The first waves of bosses begins after Mega Satan takes 750 damage, the second after 1,500 damage, and the third after 2,250 damage. He will withdraw but not spawn these waves if there are any remaining previously spawned bosses left only when the room is cleared does he spawn the following:
 * Wave 1.1: Famine and Pestilence
 * Wave 1.2: War and Death
 * There is a chance for all Horsemen to appear as their champion forms.
 * Wave 2.1: Super Envy
 * Wave 2.2: Super Lust and Super Wrath
 * Wave 2.3: Super Sloth, Super Gluttony, Super Pride, and Super Greed
 * Wave 3.1: Fallen Uriel
 * Wave 3.2: Fallen Gabriel

Phase 2
After taking 3,000 damage, Mega Satan sinks into the darkness and rises in his final phase as a skull. He no longer has his hands, nor does he spawn bosses; instead, he fires complex, projectile patterns. Possible patterns include the ones from the first phase (with increased shot speed), plus:
 * 2 spirals of projectiles that slowly rotate counterclockwise. The shots zig-zag as they travel outward.
 * 2 lines of projectiles that alternate between curving left and right. These lines combine to create curving lines with a safe space that moves from the left of the arena to the right.
 * Rings of projectiles, with every other wave fluctuating in speed as it travels.
 * Many lines of projectiles that slowly curve to the left (if black) and right (if red); these lines create safe spaces to maneuver in that slowly shift to the right.
 * Several lines of projectiles that slowly wiggle as they travel, similarly to Wiggle Worm. The angle these shots are fired at either rotates clockwise or alternates between rotating clockwise and counterclockwise.
 * Many lines of projectiles that wiggle as they travel and slowly curve to the left (if black) and right (if red); these lines create unmoving safe spaces between them.
 * Many lines of projectiles that spin as they travel, similarly to Ring Worm. The angle these shots are fired at constantly randomizes.
 * These projectiles don’t travel far enough to reach the corners of the arena if Mega Satan isn’t close to that corner.
 * Dense rings of projectiles that wiggle as they travel.
 * Several lines of projectiles that make large zig-zags as they travel.
 * Six lines of projectiles, half of which slowly curve to the left (if black) and right (if red). These lines create safe spaces that slowly move towards Mega Satan.
 * Rings of projectiles that rotate clockwise (if red) and counterclockwise (if black) simultaneously.
 * Several lines of projectiles that continuously converge onto each other.
 * The projectiles used in these patterns can be colored black, red, brown, or silver, depending on which one is used. For some attacks, they instead appear as red or yellow fire.

As Mega Satan takes damage during this phase, his skull begins to crack before eventually shattering. After this final phase is defeated, the game ends and Ending 16 plays.


 * If is unlocked, there is a 50% chance that the game does not immediately end, and Mega Satan instead drops an ending chest along with a portal. Entering the chest ends the game and plays the cutscene while entering the portal takes Isaac to.

Unlockable Achievements
These achievements are exclusive to Afterbirth, Afterbirth†, and Repentance.

Damage Scaling
Damage scaling is an unclear mechanic introduced by Nicalis in The Binding of Isaac: Afterbirth to provide a more challenging experience to the players, enabling some enemies to retaliate against high damage attacks by deploying an "armor" of a sort to greatly reduce the amount of damage taken. Further details and an in-depth explanation may be found here. Damage Scaling was given to Mega Satan and his hands in Repentance.

Trivia

 * Mega Satan's battle theme is titled Hericide, just like regular Satan.
 * The Mega Satan room is a 1x2 room with only the lower half accessible.
 * Mega Satan's second phase is referred to as "Mega Satan 2" in the bestiary.
 * Mega Satan's second phase has unused sprites of skeletal hands.