| Mega Satan|
| First phase: 3000|
Second phase: 2000
|The Chest or The Dark Room|
| N/A (Cuts directly to Ending 16)|
|Defeating ??? or The Lamb|
Mega Satan is an unlockable boss in The Binding of Isaac: Rebirth.
- ??? or The Lamb must have been defeated in an earlier run.
- Collecting both key pieces will form the fully completed key, which is automatically used upon entering The Chest or the Dark Room on the golden gate.
- Stepping on spikes in a Sacrifice Room for the 9th and 11th times spawn Uriel and Gabriel, who will drop their respective key pieces. Stepping on spikes for the 12th time and beyond has a 50% chance to teleport Isaac to the Dark Room, where the door will be unlocked if both key pieces were picked up.
Passing through this Golden Key door and stepping onto the pentagram will initiate the Mega Satan fight.
- Mega Satan has several attacks:
- He can spit out a fast 3 or 4-directional spread of blood shots, with little to no space between consecutive shots.
- He can fire a wide Brimstone beam directly downwards.
- He can repeatedly smash his head into the platform, sending scattered blood shots in all directions.
- With one hand, he can smash the platform, sending a circular wave of rocks outwards.
- He can rapidly smash both hands in front of him, sending waves of rocks forwards.
- After a certain threshold of damage, he will summon all four Horsemen of the Apocalypse in pairs, Famine with Pestilence followed by Death with War. His face and hands will be invincible while he withdraws to watch the fight.
- After another threshold, he will summon all seven super sins in three waves: Super Envy on its own, followed by Super Lust with Super Wrath, and finally Super Gluttony, Super Sloth, Super Greed, and Super Pride together.
- After a third threshold, he will summon a dark version of Uriel. After it is killed, a dark version of Gabriel will appear. The different color is purely cosmetic and both angels have the exact same behaviour as their normal counterparts.
- Taking too much time between thresholds will cause Mega Satan to start summoning normal sins and bosses, including The Hollow.
After taking even more damage, Satan will sink into the darkness and rise up in his final phase as a skull. His final form does not spawn any other enemies; instead, he fires complex, bullet hell-style shots. Possible patterns include:
- Streams of red shots
- Rings and streams of multi-colored fire
- Streams of simultaneous red and black shots, which move in different patterns
- Brown shots which split into 4 smaller brown shots, similar to Cricket's Body.
- Rings of black shots that pulse outwards
- Streams of black shots that move outwards in a Ring Worm pattern
- Streams of metallic gray shots which move outwards in a zigzag pattern
- Rings of metallic gray shots that move in a Wiggle Worm pattern
As Mega Satan takes damage during this phase, his skull will begin to crack. After this final phase is defeated, the game ends and the final ending cutscene plays.
If The Void is unlocked, there is a 50% chance that the game will not immediately end, and Mega Satan will instead drop an ending chest along with a portal. Entering the chest ends the game and plays the cutscene, while entering the portal will take Isaac to The Void.
These achievements are exclusive to Afterbirth.
- Cry Baby - Defeat Mega Satan as Isaac.
- Red Baby - Defeat Mega Satan as Magdalene.
- Green Baby - Defeat Mega Satan as Cain.
- Brown Baby - Defeat Mega Satan as Judas.
- Blue Baby - Defeat Mega Satan as ???.
- Lil' Baby - Defeat Mega Satan as Eve.
- Rage Baby - Defeat Mega Satan as Samson.
- Black Baby - Defeat Mega Satan as Azazel.
- Long Baby - Defeat Mega Satan as Lazarus.
- Yellow Baby - Defeat Mega Satan as Eden.
- White Baby - Defeat Mega Satan as The Lost.
- Big Baby - Defeat Mega Satan as Lilith.
- Noose Baby - Defeat Mega Satan as Keeper.
- Mort Baby - Defeat Mega Satan as Apollyon.
- Mega Blast - Defeat Mega Satan with every character.
- Afterbirth added Completion Marks for defeating Mega Satan. In Rebirth, there are no achievements linked to Mega Satan.
- Mega Satan does not have a health bar, making it difficult to determine how close he is to death.
- Mega Satan does not drop a Golden Chest after beating him, instead cutting directly to Ending 16.
- Unlike normal bosses, he is immune to Midas' Touch.
- Killing one of his hands deals 100 damage to Mega Satan.
- With homing tears and The Ludovico Technique, the tear will be constantly attracted by the head even when it's untargetable, making killing the horsemen, sins and angels very hard.
|Achievements||Attributes||Bosses||Cards and Runes||Challenges||Chapters|
|Chapter 1|| Blighted Ovum • Dingle • The Duke of Flies • Famine • Fistula • Gemini • Gurdy Jr. • Gurglings • The Haunt • Larry Jr. • Monstro • Pin • Steven • Widow |
Dangle • Little Horn • Rag Man • Turdlings
|Chapter 2|| C.H.A.D. • Chub • Dark One • Gurdy • Gurdy Jr. • The Hollow • The Husk • Mega Fatty • Mega Maw • Peep • Pestilence • Polycephalus • The Carrion Queen • The Wretched |
The Forsaken • The Frail • The Stain
Big Horn • Rag Mega
|Chapter 3|| The Adversary • The Bloat • The Cage • The Carrion Queen • The Gate • Gish • Loki • Mask of Infamy • Monstro II • War • The Wretched • Mom |
|Chapter 4||Blastocyst • The Bloat • Conquest • Daddy Long Legs • Death • It Lives • Lokii • Mama Gurdy • Mom's Heart • Mr. Fred • Scolex • Teratoma • Triachnid|
|Chapter 5||The Fallen • Isaac • Satan|
|Chapter 6||??? • The Lamb • Mega Satan|
|Greed Mode|| Ultra Greed |
|Chapters 1-4||The Fallen • The Headless Horseman|