Tainted Jacob is a character added in The Binding of Isaac: Repentance. He is the alternate version of Jacob. Tainted Jacob is unlocked by reaching Home and using either the Red Key or the Cracked Key to access a special room in one of the walls while playing as Jacob & Esau.
Tainted Jacob spawns with 3 red heart containers and Anima Sola in his consumable slot. Anima Sola freezes the nearest enemy for 5 seconds. However, he is pursued through the entire game by Dark Esau, who will try to charge into and kill Tainted Jacob. Anima Sola always affects Dark Esau if he is on screen.
If Dark Esau touches Tainted Jacob or if Dark Esau dies, Tainted Jacob "dies" and becomes functionally identical to The Lost, with the special properties of flight, spectral tears, and a lack of health. Dark Esau's touch effect cannot be avoided even while shielded, invulnerable, or otherwise immune to damage (such as with Holy Mantle or Gnawed Leaf). Once Tainted Jacob is in Lost form, Dark Esau's attacks affect him normally, respecting shield and invulnerability effects if he has them and killing him if he doesn’t. The flames Dark Esau generates upon spawning on a floor will simply damage Tainted Jacob rather than putting him in this state, and the death explosion from Dark Esau does not kill Tainted Jacob if he was already in his Lost state.
It should be noted that unlike the true Lost, Tainted Jacob does not have an intrinsic Holy Mantle in this form, and unless he has picked it up prior in the run, any damage taken will instantly kill him. He can, however, take devil deals for free just like the Lost. His health bar is disabled entirely during this time, meaning the effects of any items that modify his health in any way (such as health up/down pills or soul hearts) will be ignored. Hematemesis will still drain your red hearts while Tainted Jacob is in his lost form.
Upon reaching a new floor, Tainted Jacob will return to his living state.
Dark Esau spawns 20 to 40 seconds after Tainted Jacob goes to a new floor, emerging from a crack in the ground and creating rings of flame around him upon spawning. Dark Esau continuously pursues Tainted Jacob by floating towards him, speeding up if he is far behind. After getting close enough to Tainted Jacob he charges in the cardinal/ordinal direction closest to Tainted Jacob leaving behind a trail of flames that can burn enemies. Dark Esau comes to a complete stop right before reaching Tainted Jacob and maintains a distance between the two; he can only break this distance by charging at him or if Tainted Jacob walks backwards into him.
Anima Sola can restrict Dark Esau's movement for 5 seconds, and always targets him if he's alive. When released, Dark Esau always charges at Tainted Jacob immediately- charging directly at him rather than along the cardinal/ordinal directions.
Dark Esau's position at all times is determined by his position relative to the general layout of the floor, meaning he persists in the same location even when Tainted Jacob moves through rooms. However cannot be left completely behind and appears to move faster the further he is from Jacob. Moving into a new room cancels Esau's charge if he was preparing one as well as if he was bound by Anima Sola.
Dark Esau cannot be damaged by enemies or most environmental hazards except for spiked rocks, red poops and TNTs, but he can be damaged by Tainted Jacob and any active bombs and even be killed. Upon death, he creates a room-wide explosion similar to Mama Mega! that instantly "kills" Tainted Jacob, turning him into a ghostly The Lost state with no Holy Mantle (completion marks in this state will still count for Tainted Jacob). This does not affect Tainted Jacob if he’s already in a ghost state. The Mama Mega! explosion only applies to the room Tainted Jacob is in and not necessarily the room Dark Esau dies in; if Tainted Jacob goes to a new room before his death animation finishes, the explosion will trigger in the room Tainted Jacob moves to. After Dark Esau has died, he does not appear again for the rest of the floor.
Dark Esau's health increases each time Tainted Jacob progresses down a floor. His base health is calculated with the following formula: (250 + 20 x stage). For example:
During Basement Floor 1, Dark Esau has (250 + 20 x 1) = 270 HP.
During Caves Floor 1, Dark Esau will have (250 + 20 x 3) = 310 HP.
By Womb Floor 2, Dark Esau will have (250 + 20 x 8) = 410 HP.
Dark Esau is able to damage enemies as well as Tainted Jacob in the following ways:
He creates 12 rings of 8 flames when he spawns, each dealing 6 damage to enemies they hit, dealing anywhere between 6-576 damage depending on how close they are to him. These flames can be blocked by obstacles.
He deals 30 contact damage per tick to enemies and pushes them (60 damage per second).
He deals an extra 10 damage per tick to enemies and inflicts Burning on them when leaving a flame trail while charging at Tainted Jacob (300 damage per second).
Finally, the explosion he creates when he dies deals 200 initial damage plus an additional five ticks of 25 damage to all enemies in the room, for a total of 325 damage.
Tainted Jacob is constantly chased by Dark Esau, and there are almost no effective ways to rid of him without a downside due to Dark Esau's death effect, which turns Tainted Jacob into a temporary The Lost form. Because of this, playing as Tainted Jacob requires the player to manage both the playable Jacob and the AI Esau, which can make this character one of the hardest to play.
Using Anima Sola is key to success for Tainted Jacob, as it can prevent a lot of close calls and position Dark Esau to be used as a weapon of sorts. As Anima Sola charges immediately after being activated, it can be used in two ways: holding Dark Esau stationary for its duration which allows Anima Sola to charge for several seconds, or using Dark Esau immediately as a projectile at the cost of waiting the full cooldown duration.
Unless in ghost form, contact damage from Dark Esau is unavoidable and pierces through all invulnerability effects, including invincibility after getting hit. As such, do not save invulnerability items to avoid Dark Esau.
If Dark Esau is in the process of traveling between rooms, it is possible to use Anima Sola to chain him outside of the current area Jacob is in. Most of the time, his charge won't even be able to reach close enough to the player to hit him, although precaution should still be taken in the event it does. This knowledge is especially useful since accidentally killing Dark Esau (and therefore turning into The Lost) with a really strong build can become a problem in the late game. Chaining him outside of the room gives a moment to deal as much damage as possible without him getting in the way and accidentally getting hit.
It may be useful to swap the spacebar and Q keys, allowing the player to activate Anima Sola without having to move a finger off of their movement keys. This makes binding and releasing Dark Esau to be easier and faster. However, this will likely mess with the player's muscle memory, so it can take some practice to get used to.
Dark Esau
As Dark Esau takes around a minute to spawn, Tainted Jacob should aim to explore as many rooms as he can before Dark Esau spawns and becomes a persistent problem.
Dark Esau's spawn and movements are relative to the entire floor's position even as Tainted Jacob moves through rooms. This means that he will take much longer to catch up if Jacob teleports a long distance, or end up spawning right near a door if he manages to charge into one that Jacob moves into. Gauge this properly to prevent accidental incidents where Jacob ends up running right into Dark Esau; it is wise to wait till Dark Esau moves back into the current room, then circle around him before entering a new room.
Dark Esau will speed up when further from Jacob, and slows down to almost a standstill when close. This means he will always keep a consistent distance from him. Dark Esau will never actually be able to contact Jacob unless he starts his charge animation, charges, or Jacob runs backwards into him. In some cases such as being next to an obstacle, Dark Esau will stop moving within the prop and will be unable to charge until Jacob moves away from it.
Considering the damage Dark Esau can deal to enemies and the fact that Anima Sola can be canceled early by using it a second time, Dark Esau can become a powerful but very dangerous weapon to use against enemies by positioning Tainted Jacob in ways that manipulate him into charging into enemies.
Dark Esau's charge is able to single-handedly kill most early bosses in one or two hits. He can also be held in place with Anima Sola to bait chasing enemies, as Jacob can stand behind Dark Esau and cause them to run into him.
Dark Esau does not take damage from enemies nor enemy-generated troll bombs, but does take damage from environmental hazards such as spiked rocks, red poop and explosive hazards. Ensure to keep him away from these to prevent untimely deaths.
Some obstacle rooms have large amounts of exploding barrels or explosive rocks. This can result in Dark Esau taking tons of damage.
Dark Esau's charge will extinguish Fire Places without hurting him. He will not detonate TNT or bomb rocks.
While Dark Esau's health is extremely high and goes up with each floor, his health increase is usually not significant enough to help him survive when the player has obtained multiple damage upgrades. Players should be wary of accidentally killing Dark Esau during endgame fights such as Mega Satan, and use Anima Sola to position him away from Jacob's tears.
In Greed Mode, Anima Sola will always be charged at the beginning of a new wave. This can be taken advantage of by binding Dark Esau before a new wave begins and then letting him charge into a freshly spawned enemy group or a priority enemy like a champion. Since releasing Dark Esau manually does not consume the item charge, the item will still be available to restrict him again immediately afterwards.
Dark Esau's Death
Upon his death, Dark Esau causes a massive explosion that acts like a single-room Mama Mega!. This causes all its effects in the room he is in: this includes destroying every prop, bombing the Donation Machine, doing extreme damage to all enemies, and breaking every door. This explosion can even open the doors to Boss Rush and Template:Stage.
Dark Esau's death explosion causes Jacob to become a special version of The Lost for the rest of the floor, just like getting contact damage from him. While this is usually always detrimental since any hit will kill Jacob afterwards, it is possible to safely use Lost Jacob after clearing the whole floor to collect stray pickups which may be unreachable in normal mode. Dark Esau's explosion can also be used for last-resort damage against a boss if needed.
In ghost form, Tainted Jacob's health cannot be healed. Red hearts cannot be picked up by him, and all other hearts (including eternal hearts) do not grant anything even if Jacob progresses to the next floor.
Item Interactions
Most targeting items will not target Dark Esau despite him being an enemy. Kill-activated items will also activate if Dark Esau kills enemies.
While in his Lost form, Tainted Jacob can take devil deals in the same way as the Lost.
As such, the Satanic Bible is a very good pickup as it essentially swaps out boss room items for Devil room items.
Even in his Lost form, Tainted Jacob can gain broken hearts from effects such as VI - The Lovers?, Heartbreak and Magic Skin, but they are not shared between forms. Additionally, unlike the true Lost, Magic Skin can be used up to 12 times by Tainted Jacob instead of once.
In Co-Op mode, the flames Dark Esau creates upon spawning can damage other players, but he otherwise ignores them completely.
If multiple players are playing Tainted Jacob, then any Tainted Jacob who touches any Dark Esau will still be turned into a ghost or die. Tainted Jacob players will only be able to use Anima Sola on their own Dark Esau, and if one of the Tainted Jacobs is completely killed both Dark Esau's will begin to target the one that is still living.
When Tainted Jacob completely dies and is turned into a small ghost baby as a Co-Op partner, if no other Tainted Jacob players are in the match then Dark Esau will still follow the ghost of Tainted Jacob, allowing them to still use him as a high damage weapon to help their teammates.
In Co-Op mode, if Tainted Jacob was turned into his ghostly form by Dark Esau, then dying and being revived upon completion of the boss will have him revive as his ghostly form.
If Tainted Jacob is dead at the start of a floor, Dark Esau will still spawn but will target one of the living players instead. Unless they are also playing Tainted Jacob, he will never hurt them outside his spawning animation.
Like every other "boss", Dark Esau can be spawned with debug commands. However, if playing as someone other than Tainted Jacob, the player will be immune to his attacks.
Jacob, even in his normal non-tainted form, is an exception. When touched by Dark Esau, he will take damage, but will not turn into a ghost. Esau, like most characters, is still immune to Dark Esau.
When the console command "restart 39" is loaded, the player will be spawned as a ghostly version of Tainted Jacob. The only differences is that Dark Esau never seems to spawn and that this version of Tainted Jacob has the health of The Lost.
Good Items
2Spooky/Venus: Dark Esau has a chance to become feared or charmed (respectively) when approaching Tainted Jacob, making him charge away from Tainted Jacob or attack other enemies.
9 Volt: Reduces the charge time of Anima Sola by half, giving the player much better control of Dark Esau, or the ability to chain down enemies and bosses much more often if Dark Esau has already been killed.
Belly Jelly: The 50% chance to avoid damage still applies to Dark Esau, potentially saving Jacob from death/being turned into the Lost.
Black Hole: Pulls every enemy in the room and Dark Esau into one place, forcing Dark Esau to deal contact damage to all of them. However, multiple uses on the same floor can kill Esau if not careful.
Dad's Ring: Can petrify Dark Esau every 7 or so seconds.
Dark Arts: The invincibility and stunning effect fully work on Dark Esau even if he charges at the player, allowing Tainted Jacob to phase through him avoiding becoming the lost or preventing fatal damage in a pinch. Of course, this still deals damage to him, so use caution.
Dead Cat: If picked up in ghost form, Jacob will retain all his health, though any deaths will cause him to respawn in ghost form. Once he progresses to the next floor, he will respawn with his body and with all health containers remaining.
If Lost Jacob dies with Dead Cat, Tainted Jacob's health won't go to the usual one heart container after the resurrection but three. The effect can be only observed when going to another floor, and changing back to Tainted Jacob.
Eraser: Removes Dark Esau from the rest of the run so long as the killing blow is done by the Eraser; this causes subsequent spawns to be replaced with a puff of smoke. This requires Dark Esau to have less than 15 HP; if he has too much health, the Eraser will simply do 15 damage. Eraser will also fail if it is thrown during Dark Esau's death animation.
Esau Jr.: Switching between Jacob and Esau Jr. will cause Dark Esau to despawn. He will reappear after 30 seconds as either character, but switching will always reset the timer. Esau Jr. does not turn into the Lost upon contact with Dark Esau, but takes half a heart damage instead. Switching back to Jacob from Esau Jr. also prevents Dark Esau from turning Jacob into the Lost.
Error: The given collectible ("Glowing Hour Glass") does not exist.: Very useful. Using it will return Jacob to his regular form in the previous room, if he was turned into the lost. It also can allow to kill Dark Esau without transformation into a ghost - to do so, you need to kill Dark Esau in one room, then, before Dark Esau ended his death animation, go to the other room, wait till explosion will transform you into the ghost, and then use Glowing Hour Glass. That way you will return to your normal form, and Dark Esau will not be respawned.
Heartbreak: Will allow Jacob in his Lost form to avoid death up to 5 times, the 6th hit will kill Jacob.
Holy Mantle: While the shield does not guard from Dark Esau at first, it does protect him in his Lost form, helping Jacob survive after being turned into the lost.
How to Jump: Jumping allows Jacob to bypass Dark Esau.
Jacob's Ladder: Electricity will not target Dark Esau even if Jacob's tears hit an enemy.
Magic Skin, and likewise VI - The Lovers? will allow Jacob to generate items for free if he is in his Lost form.
Punching Bag: When Dark Esau spawns, there is a chance he may target the Punching Bag instead of Jacob. So long as Anima Sola is not used, he will never retarget Jacob, making him endlessly attempt to kill the Punching Bag until the next floor, where he may swap targets on spawning in.
Satanic Bible : Allows Jacob to get turned into his Lost form intentionally to receive free Devil Room items every floor.
Sigil of Baphomet: Kills made by Dark Esau will also trigger a temporary shield.
Spider Mod: Does cause status efffects to Esau on contact like confusion which helps to disrupt his pursuit of Jacob. Lets Jacob keep track of Dark Esau's health. Especially useful if the player wants to remove Dark Esau with the Eraser. (Likely due to bug it does not always display health bar.)
Bad Items
Acid Baby: Whenever Jacob uses a pill, Dark Esau will be poisoned.
Akeldama: The tears generated while in a hostile room will hit Dark Esau plenty of times.
Angry Fly: Will chase only Dark Esau whenever possible.
Athame: The Brimstone ring will deal great amounts of damage to Dark Esau.
Big Chubby: The inaccurate nature of this familiar can lead to unintentional damage dealt to Dark Esau.
Book of Virtues: The wisps generated from Anima Sola will target Dark Esau and damage him, while other wisps generated from Book of Virtues will often make contact with Dark Esau, damaging him further.
Brown Nugget: The stationary flies produced will target Dark Esau and deal damage to him, making this a risky item to use.
Curse of the Tower: Dark Esau can still be damaged by the troll bombs, despite being immune to other troll bombs. Combined with other bomb items, such as Bob's Curse or Sad Bombs, Dark Esau's death is inevitable if Jacob gets hit by another enemy.
Dead Tooth: The toxic aura will poison Dark Esau whenever he comes in contact with Jacob.
Depression: Whenever Dark Esau makes contact with the cloud, he will be hit with the beam of light, causing massive damage.
Error: The given collectible ("Guppy's Hair Ball") does not exist.: This item becomes extremely hard to utilize with Dark Esau present, and will most likely end up damaging and/or killing him.
Isaac's Heart: Dark Esau no longer kills Jacob if he touches his body, but contact with the heart will. This makes it far easier to die since both Isaac's Heart and Dark Esau's default positions are behind Jacob, and causes them to collide very frequently.
Jupiter: Whenever Jacob attempts to move away from Dark Esau, he will poison him.
Lil Abaddon: The Brimstone ring will deal damage to Dark Esau.
Linger Bean: If Jacob is not careful, Dark Esau will often make contact with the clouds left from firing, damaging him.
Lost Soul: The soul can be killed by Dark Esau, making it very difficult to keep it alive, unless Jacob has BFFS!.
Maw Of The Void: The Brimstone ring will deal damage to Dark Esau.
Mom's Razor: The damage and bleeding dealt from this familiar can kill Dark Esau quicker than desired.
Monstrance: The aura damages Dark Esau, leading to his quick death.
Montezuma's Revenge: Jacob must be extremely precise to not unintentionally damage Dark Esau.
Obsessed Fan: The fly will almost always be in contact with Dark Esau, making his death inevitable before the end of the floor.
Pointy Rib: Jacob must be extremely careful, otherwise Dark Esau can take massive damage from the rib.
Pop!: With a high fire rate, many eyeballs will fill the room, dealing unintended damage to Dark Esau.
Sacrificial Dagger: The damage dealt from this orbital can kill Dark Esau quicker than desired.
Samson's Chains: It is very difficult to avoid hitting Dark Esau with the ball, which will inflict plenty of damage.
Saturnus : The ring of tears can damage Dark Esau.
Shade: The shadow will follow Jacob's movements with a delay, which unluckily is the path that Dark Esau usually takes to catch up to Jacob. This results in Dark Esau taking a lot of damage simply from following Jacob.
Sharp Straw : Damages Dark Esau, alongside the rest of the room, too many uses on a floor can unintentionally kill him
Tiny Planet: The pattern that Jacob's tears follow make it difficult to not hit Dark Esau when in combat.
Vasculitis: Both Jacob and Dark Esau killing enemies will create a burst of tears, which Dark Esau will often take damage from.
Situational Items
7 Seals: War and Death will chase after Dark Esau, but the rest of the harbingers and the locusts won't.
Demon Baby: The familiar will not target Dark Esau, but can still damage him with shots if he runs into them.
Cube Baby: The baby can damage Dark Esau, but will not do much damage. Dark Esau can also "kick" the baby into enemies.
Immaculate Heart: The halo of tears will lead to Dark Esau often being hit.
Lil Delirium: Delirium will turn into familiars that can target/damage Dark Esau.
Ocular Rift: The rifts do not damage Dark Esau, and can cause him to make contact with many enemies. However, the speed at which Dark Esau is pulled into the rifts can cause Jacob to get hit by him.
Gallery
Tainted Jacob's ghostly version.
Trivia
Dark Esau may be based on a story in the Book of Genesis, in which Esau attempts to kill Jacob after both Jacob and their mother tricked their father Isaac into giving Jacob a blessing intended for Esau, resulting in Jacob fleeing from Esau's wrath.
This is also further backed up by Tainted Jacob's unlock achievement name, "The Deserter."
Dark Esau acts similarly to the Lord of the Jammed from Enter the Gungeon, an invulnerable enemy which constantly chases and attacks the player once they've acquired enough curse points.
Big Horn's hand can be seen during Dark Esau's death animation, coming out of a pit and dragging him down.
Bugs
Bug!
If you save and reload after Tainted Jacob has been changed into his lost form, he will not switch back when changing floors, and Dark Esau will no longer spawn.
Bug!
If you reroll your items before Dark Esau spawns (with the help of either the D4, D100, D infinity or the Dice Room), he will not appear on the current floor.
Bug!
If you exit to the menu during Dark Esau's death animation he will no longer spawn until the next floor and Tainted Jacob will stay in his natural form.
Bug!
In Co-Op, if Tainted Jacob is dead but Dark Esau explodes, then his ghost baby will appear to die and become a floating Isaac head. This is purely cosmetic.
Bug!
Using Clicker as Tainted Jacob while Dark Esau is present will crash the game.
Bug!
Becoming Tainted Jacob by using Clicker will cause Dark Esau to not spawn for the current floor. Dark Esau will spawn as normal on the next floor.
Bug!
If you use the Meat Cleaver on Dark Esau, his death explosion will not turn you into Tainted Jacob's Lost form.
Bug!
If you defeat Dark Esau and die from his explosion after exiting to an already cleared room, you can use Error: The given collectible ("Glowing Hour Glass") does not exist. to change back to his original form without Dark Esau spawning again for the floor.
Bug!
In Co-Op, if Tainted Jacob is revived after the boss' defeat in his ghostly form and is killed by Dark Esau, then his ghost baby on the next floor will have glitched sprites and appear as a disembodied Isaac head. When walking left, Isaac's head will be replaced by a headless body repeating the downwards walk cycle.
Bug!
If Dark Esau is alive when Mega Satan attempts to spawn the Harbingers, Mega Satan will become invulnerable like normal, but the Harbingers will not spawn. The only way to progress is to kill Dark Esau.
Bug!
If Error: The given collectible ("Glowing Hour Glass") does not exist. is used the room after Dark Esau spawns, Daddy Longlegs will proceed to target Dark Esau. This persists between floors.
Bug!
If Dark Esau is still alive, killing certain bosses such as It Lives or Ultra Greed will kill Dark Esau instantly, even if he was at full health.
Bug!
If you pick up Abaddon as lost form, Tainted Jacob will not switch back when changing floors, and Dark Esau will no longer spawn.
Jacob. Tainted Jacob is unlocked by reaching 
Home and using either the 
Red Key or the 
Cracked Key to access a special room in one of the walls while playing as Jacob & Esau.
Anima Sola in his consumable slot. Anima Sola freezes the nearest enemy for 5 seconds. However, he is pursued through the entire game by Dark Esau, who will try to charge into and kill Tainted Jacob. Anima Sola always affects Dark Esau if he is on screen.
The Lost, with the special properties of flight, spectral tears, and a lack of health. Dark Esau's touch effect cannot be avoided even while shielded, invulnerable, or otherwise immune to damage (such as with Holy Mantle or 
Gnawed Leaf). Once Tainted Jacob is in Lost form, Dark Esau's attacks affect him normally, respecting shield and invulnerability effects if he has them and killing him if he doesn’t. The flames Dark Esau generates upon spawning on a floor will simply damage Tainted Jacob rather than putting him in this state, and the death explosion from Dark Esau does not kill Tainted Jacob if he was already in his Lost state.
Holy Mantle in this form, and unless he has picked it up prior in the run, any damage taken will instantly kill him. He can, however, take devil deals for free just like the Lost. His health bar is disabled entirely during this time, meaning the effects of any items that modify his health in any way (such as health up/down pills or soul hearts) will be ignored. Hematemesis will still drain your red hearts while Tainted Jacob is in his lost form.
Esau.
Mama Mega! that instantly "kills" Tainted Jacob, turning him into a ghostly 
Basement Floor 1, Dark Esau has (250 + 20 x 1) = 270 HP.
Bug!
D4, 
D100, 
D infinity or the Dice Room), he will not appear on the current floor.
Clicker as Tainted Jacob while Dark Esau is present will crash the game.
Meat Cleaver on Dark Esau, his death explosion will not turn you into Tainted Jacob's Lost form.
Daddy Longlegs will proceed to target Dark Esau. This persists between floors.
Characters 
Mini-Bosses 
Lust • 
Gluttony • 
Greed • 
Sloth • 
Wrath • 
Envy • 
Pride
Super Lust • 
Super Gluttony • 
Super Greed • 
Super Sloth • 
Super Wrath • 
Super Envy • 
Super Pride • 
Ultra Pride
Devil Room / 
Angel Rooms
Krampus • 
Uriel • 
Gabriel
Mother's Shadow • 
Dark Esau
The Binding of Isaac: Rebirth
