Tainted Eden is a character added in The Binding of Isaac: Repentance. They are the alternate version of Eden. Unlike other Tainted characters, Tainted Eden has no obvious changes to their physical appearance. Tainted Eden 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 Eden.
The rerolls will easily remove health, but not restore it. This makes it risky to focus solely on red hearts or soul hearts, and a balanced approach is overall safer.
Removal of items with heart containers while Tainted Eden has no red hearts would not deplete soul hearts or bone hearts, which means making devil deals with heart container items could be much more worthwhile.
However a roll that fills the health bar with red hearts and overwrites soul hearts, followed by one that removes them may be dangerous.
Powerful transformations such as Guppy are difficult to attain, as transformations are removed with the items, and will not be restored if you roll back into the items.
Shops are worth investigating, as they are the only source of Birthright that will lock the current set of items. However, Birthright cannot be rerolled into and gathering shop items for rerolling will not work.
If Gulp! pills or a Smelter are available, absorbing trinkets makes them permanent. If possible, they should be discarded to avoid losing them to a reroll while looking for better trinkets.
Each item is always re-rolled into the same item (at least within a given seed and floor). For instance, reverting a re-roll with Glowing Hour Glass then getting hit will always give Tainted Eden their Glowing Hour Glass back.
Since cards and pills are re-rolled on hit, it is recommended to pick up 0 - The Fool before the fight with Mom and drop it before her stomp to start the Ascent route.
Missing No. will not be rerolled upon taking damage, but can be rerolled into.
Spending health on a Devil Beggar will always trigger a re-roll.
Birthright will prevent the currently held active item from rerolling. However, if it is replaced, active items (including the original) will continue to be re-rolled.
Strategy
Keeping some soul hearts or black hearts is beneficial because those cannot be rolled away.
If you do happen to see Birthright in a shop, consider whether the item set that you have so far is something you want to lock in for the rest of the run. If it's not, and if you have durable health to spare (from soul hearts or from permanent sources like eternal hearts or Health Up pills), you might want to consider taking damage a couple times to see if your items reroll into something better.
This can be especially effective if you have items from the Angel Room Item Pool or the Planetarium Item Pool, if you can lock a powerful item like Revelation orGodhead that can make for a much more effective run. If this floor has any curse room items or devil room items this may be the one time it's consistently beneficial to take those, since Birthright will prevent those from rerolling into Dead Cat if you collect it just after.
Gaining heart containers from sources other than passive items, such as Health Up pills or Eternal Hearts is beneficial, because those changes are not rolled away.
More than other characters, Tainted Eden benefits from quantity over quality of individual items since the items are likely to get rerolled several times anyway. Buying as many passive items as you can find, and picking up every passive item from safe item pools, gives more items to reroll and more chances of useful synergies.
Diplopia can be useful for doubling any passive item, because both will be rerolled into separate items.
Getting items from more consistently positive item pools can make a big difference. In particular, Angel Room items and Planetarium items usually reroll into their own item pools, almost all of which are beneficial and some are particularly powerful.
Avoiding Devil Room and Curse Room passives might be a good idea to reduce the chance of rerolling into a detrimental item like Dead Cat. It will remove all red health and grant nothing in exchange - the extra lives are likely to be lost from the first hit taken.
If you have Missing No. or TMTRAINER unlocked you may also want to avoid taking Secret Room items, as rerolling into them can add even more unwanted unpredictability to your run.
An alternative strategy to avoiding Devil Rooms is to take as many Devil items as possible, to get rid of as many red hearts as you can - You won't have to worry about your red hearts being rerolled away if you're not relying on them to begin with. It requires more skill to depend mainly on soul hearts, however.
It can be beneficial to carry a trinket even if it's not one you would normally bother with, because if you are carrying a trinket the trinket will also be rerolled when you take damage.
If you find a pill or a card that you want to save for more effective later use, like I'm Drowsy..., Full Health, The Sun, or Chaos Card, you might want to drop it at the beginning of each floor and then go back to pick up before proceeding to the next floor to prevent rerolling it.
It can be beneficial to carry bad pills and other consumables you don't intend to use because they may be rerolled into something good.
Curse room and Red Chest Actives will frequently roll into Guppy's Paw, allowing empty hearts from rerolls to be turned into soul hearts.
Angel room actives can reroll into Eden's Soul, granting two items from a particular pool, while Secret room actives can be rerolled into R Key or Death Certificate.
Angel items can be rerolled into Eucharist for a boss room and The Stairway before going down a floor, allowing Eden to reliably gain more angel items.
Libraries can be powerful for Tainted Eden. If Book of Virtues is acquired from a library, it cannot be rerolled by damage as Book of Virtues is the only passive item in the library pool.
Holding NO! when taking a hit will turn your active item into a passive item. This may or may not be desirable, so when trying to reroll an active into something specific, it's advisable to drop the current trinket.
Plenty of trinkets don't need to be held constantly to benefit from their effects, so dropping them when they aren't needed is often advisable. In particular, trinkets that affect level generation like Bloody Crown, Telescope Lens and Fragmented Card can be dropped in the starting room of each floor, and only returned to once ready to proceed to the next.
Items
While "good items" and "bad items" are less of a factor of choice than for other characters since they are frequently rerolled, there are some that should be of special notice if found or rerolled into.
Good Items
Stitches: Can be used strategically by entering curse rooms with the invincibility granted by teleporting, and to teleport onto and damage or kill enemies.
Death Certificate: Allows Tainted Eden to get Dogma, which will be a permanent damage up and flight.
Abyss: Can be rerolled, but the locusts are permanent.
Book of Revelations: Adds soul hearts which are a relatively stable form of health for Tainted Eden.
Birthright: Prevents items acquired before Birthright was picked up from being rerolled. This includes normal rerolls from items like D4 and Missing No., not only the damage-triggered rerolls.
Rock Bottom: Not much use by itself due to the loss of its effect once rerolled. However, if Rock Bottom is obtained and then 'locked in' with Birthright, it would keep the best value of each stat for every stat reroll and item synergy rerolled for the rest of the run.
If Birthright is discovered in a shop it might be worth taking damage a few times to try to reroll a powerful synergy before locking it in with Birthright.
Converter: Grants red hearts which won't be rerolled away, significantly improving Eden's effective health for the rest of the run.
Glowing Hour Glass: If used after getting hurt in the same room, will return Tainted Eden to their previous build upon landing in the previous room. Should Tainted Eden get hurt again while holding their previous active item, they will always reroll it into Glowing Hour Glass. Knowing this, players can practice a room in which they got hurt once until they clear it perfectly, and keep the prior item set as long as they keep using this strategy.
Holy Mantle: Triggering Holy Mantle will not trigger rerolls, helping Tainted Eden keep their current build.
Blanket: Serves as a weaker version of this, for boss battles only.
Placenta: If this item is rolled into while Tainted Eden possesses empty red heart containers, it may be wise to idle in cleared rooms until reaching max health. From there, Placenta is not likely to be useful since damage will reroll it anyway.
Prayer Card: If retained long enough to be used a few times, Tainted Eden will be able to gain significant permanent health, which is hard to come by for this character.
Purgatory: The effect will remain for the current room even if the item itself is rerolled through damage, providing a helpful boon during boss battles.
Red Stew: The temporary damage boost is retained even after the item is rerolled, potentially acting as a semi-permanent item effect until the damage boost is lost completely.
The orbital flies granted by The Swarm do not disappear if the item is rerolled.
Lil Clot will persist after the trinket is dropped, acting as a semi-permanent familiar until it dies
Dad's Lost Coin although the item is not very useful, it does drop a permanent luck upgrade in the form of a Lucky Penny.
Bad Items
Dead Cat: Removes all red heart containers, even from sources that are otherwise more durable for Tainted Eden, like eternal hearts and Health Up pills, with zero benefits received in return since the extra lives will be rolled away.
Any items from the Curse Room, Red Chest, or Devil Deal item pools can reroll into Dead Cat.
Shard of Glass: The bleeding effect from taking damage will still apply even if Shard of Glass is rerolled, resulting in eventual, constant rerolls unless Tainted Eden picks up a red heart.
TMTRAINER: All items picked up after an item that ends up rerolling into TMTRAINER will become glitched items. Glitched items will not reroll anymore and will frequently be detrimental with their completely random effects.
Any passive items from the Secret Room item pool can reroll into TMTRAINER if it is unlocked. As such, it is recommended to only defeat The Beast with Tainted Eden after finishing everything else, so that Secret Room items will be safe to pick up.
Situational Items
Potato Peeler: Potato Peeler will trigger the damage randomization, but the Cube of Meat granted is permanent.
Satanic Bible: Provides black hearts which are a relatively stable form of health for Tainted Eden. However, using it will also replace the floor's boss item with a Devil deal, which should generally be avoided. No boss items means fewer overall items to reroll, ultimately reducing the chances of rerolling into great synergies.
Brittle Bones: Removes all red health but grants 6 bone hearts. Can be very strong if taken early or if low on heart containers. On the other hand, if Tainted Eden has a lot of permanent red heart containers from Eternal hearts and Health Up pills, it could be detrimental.
Guppy's Paw: Converts one Red Heart Container into three Soul Hearts. Obtained early enough in a run, it allows for Heart Containers that are granted by items that are likely to be rerolled into soul hearts that can not be rerolled. Because it is an active item, it also can not reroll into Dead Cat On the other hand, there are other ways to get permanent Red Heart Containers, and this item could remove them later in the run.
The achievement for unlocking Tainted Eden is "The Capricious", a possible name for the character.
"Capricious" means "given to sudden and unaccountable changes of mood or behavior," fitting Tainted Eden's concept of complete randomness.
Unlike regular Eden, Tainted Eden has only 1 hairstyle.
In-development, Tainted Eden's effect was a full reroll upon acquiring a new item that excluded the item triggering the reroll rather than having the reroll be triggered by damage. This was changed because in testing players would simply stop picking up items once they found something good enough to be worth keeping[1].
Gallery
Tainted Eden's transition screen portrait, identical to regular Eden's.
Bugs
Bug!
Tainted Eden consumes Eden tokens at an unpredictable rate: sometimes only one is removed, sometimes two, and sometimes more. The exact reasons and conditions are unknown.
Bug!
If Tainted Eden is firing Technology 2 when damage triggers a reroll, sometimes the laser persists firing in the last-fired direction until leaving the room, even picking up new synergies as other items reroll.
Bug!
If Tainted Eden is the first tainted character unlocked by the player, running out of Eden tokens and selecting "Random" on the tainted character screen will always pick Tainted Jacob.
Bug!
If the active item is rerolled into Alabaster Box it will be fully charged instead of discharged as usual.
Bug!
If Tainted Eden is resurrected during a Co-op game after dying, their graphics will break, cycling between Isaac's head and body.
Eden. Unlike other Tainted characters, Tainted Eden has no obvious changes to their physical appearance. Tainted Eden 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 Eden.
Birthright that will lock the current set of items. However, Birthright cannot be rerolled into and gathering shop items for rerolling will not work.
Bug!
Alabaster Box it will be fully charged instead of discharged as usual.
The Binding of Isaac: Rebirth 
Achievements
Attributes
Bosses
Cards and Runes
Challenges
Chapters
Characters
Co-op
Items
Item pools
Monsters
Objects
Pickups
Pills
Rooms
Seeds
Transformations
Trinkets
