Satan is the boss of 
Sheol, which can be accessed by either killing Mom's Heart 11 times and proceeding to kill It Lives, or entering a Devil Room after killing Mom's Heart and walking into the trapdoor that appears. It is also accessible by using 
We Need To Go Deeper!, 
Rune of Ehwaz or 
Mom's Shovel. He is the final boss of Ending 12.
Behavior
The battle against Satan has three distinct phases.
First phase
The first phase starts with a slight delay after Isaac enters the room:
Satan will shout, and roughly two seconds after Satan's voice dies out, The Fallen will spawn at the center, with two Kamikaze Leeches to both of his sides.
Once The Fallen is dead, the second wave starts.
It is advisable to place a bomb at the center shortly before the spawn: When timed right, the explosion will kill both Leeches and the first phase of The Fallen immediately. The best way to do this is by placing the bomb shortly after the sound effect that plays upon entering the room ends.
Second phase
Once this is done, Satan will appear/spawn from the statue at the top of the screen in his first form. He stays at the top of the screen, hence bombs are very effective against him. However, if he moves to the side, the bomb will be ineffective.
Patterns
- He will frequently shoot waves of projectiles from both his hands towards the left and right side of the room. The safest spot is directly in front of Satan, but beware of his
Brimstone attack. - He can shoot two slightly homing Brimstone lasers (like The Adversary) from his hands when Isaac is on the right or the left in front of Satan. The safe spot, in this case, is the center or either corner of the room.
- When Isaac is at the center of the room, Satan will start an audible charge and emit one thick straight Brimstone beam through his mouth.
- Two scattering shots of 5 and 4 projectiles from Satan's mouth, similar to Gurdy's birthing attack, except aimed directly at Isaac. This attack is virtually unpredictable and thus is very difficult to avoid.
Once he gets to a third of his life, he enters in his second form, the third phase.
Third phase
He attacks by stomping Isaac with both of his feet, which come down considerably quicker than Mom's foot. However, the stomps will come down in a constant rhythm: His second hoof follows shortly after the first one, and he redraws each after they have been on screen for about one second (like Mom's foot). Then he will stomp again about two seconds after the second foot has been redrawn.
Up to two Kamikaze Leeches will also spawn during this time. If one of them dies, another one will respawn shortly afterwards.
This can be used to your advantage to have Satan stomp on one of them for considerable damage. However, be very careful not to run into them while evading the feet, which often turns out to be the hardest part of the fight due to their charge attack, their tendency to be obstructed by the legs, as well as the random location new leeches can unexpectedly respawn.
Once Satan dies, the Kamikaze Leeches spawned by him will automatically explode and die as well.
Gallery
Satan ingame.
Satan in his second form.
Satan as one of Delirium's forms.
Unlockable Achievements
- I RULE! - Defeat ??? or The Lamb, defeat Satan as Isaac, and unlock The Negative Defeat ??? or The Lamb, and defeat Satan as Isaac Defeat Mega Satan and unlock The Negative.
Defeat 
Defeat 
Defeat - Judas - DefeatSatan.
- The Negative - Defeat Satan 5 times.
- Mom's Knife - Defeat Satan asIsaac.
- Guardian Angel - Defeat Satan asMagdalene.
- A Bag of Bombs - Defeat Satan asCain.
- Judas' Tongue - Defeat Satan asJudas.
- Forget Me Now - Defeat Satan as???.
- Blood Rights - Defeat Satan asSamson.
- Daemon's Tail - Defeat Satan asAzazel.
- Broken Ankh - Defeat Satan asLazarus.
- Book of Secrets - Defeat Satan asEden.
5 / 
9 (except 
Also, beating Satan with a particular character for the first time will unlock the inverted cross Completion Mark on that character's post-it note.
Notes
- Every time Satan is defeated, the current savefile's image changes until The Negative is unlocked.
- Using the The Bible on Satan will instantly kill Isaac, even if Isaac has the The Wafer.
- On the third wave, Pyromaniac and/or Host Hat will be extremely useful, as Kamikaze Leeches and stomping (which is considered as an explosion) will not hurt Isaac.
- Unlike in the original Binding of Isaac, Satan's feet don't cause damage on contact for the short time they rest on the ground after a stomp, providing a window of opportunity to deal significant damage with orbitals such as Sacrificial Dagger, or activate other contact effects like Midas' Touch.
Unlike in the original Binding of Isaac, Satan's feet don't cause damage on contact for the short time they rest on the ground after a stomp, providing a window of opportunity to deal significant damage with orbitals such as 
Trivia
- Satan appeared in the Halloween Update for the original The Binding of Isaac.
- Satan's pose as a statue and during the VS Screen is a nod to the demon Baphomet, who is usually portrayed in a similar pose.
- The demonic speech Satan shouts at the start of his first phase reuses one of Mom's voice lines, shouting "Isaac!" in reverse with heavy distortion.
- The music that plays during this battle is titled Hericide. Hericide is the act of murdering one's own master, lord, or teacher.
- This music also plays during the battle against Mega Satan.
- This music also plays during the nightmare wave of Greed Mode, for unlocking the floor's Devil Room or Angel Room.
 The Binding of Isaac: Rebirth
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