Tainted Eden is a character added in The Binding of Isaac: Repentance. They are the Tainted 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.
Every time they take damage, all of their stats, items (passive and active), their trinket and their currently-held card or pill get re-rolled. Items are guaranteed to re-roll into other items from the item pool they were obtained from.
The re-rolls 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.
Powerful transformations such as Guppy are difficult to attain, as transformations are removed if the appropriate items are re-rolled, and will not be restored if the items are re-rolled back into (only by manually picking up the appropriate items will re-enable the transformation).
Shops are worth investigating, as they are the only way to obtain Birthright. Birthright cannot be obtained by re-rolling into it; it must be bought the conventional way.
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 re-roll 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, Tainted Eden should pick up 0 - The Fool before the fight with Mom and drop it at the beginning of the battle, so as to not lose it if they take damage, if they intend to use it to open A Strange Door.
Missing No. will not be re-rolled upon taking damage, but can be re-rolled into.
Birthright will prevent the currently held active item from re-rolling. However, if it is replaced, active items (including the original) will continue to be re-rolled.
Keeping some Soul Hearts or Black Hearts is beneficial because those cannot be rolled away.
Obtaining Birthright may not be in Tainted Eden's best interest if the items they have acquired so far are of low quality. Deliberately taking damage, if it can be afforded, to re-roll into better items, and then taking Birthright, should be considered.
Gaining Heart Containers from sources other than passive items, such as Health Up pills or Eternal Hearts is beneficial, because those changes are not affected by Tainted Eden's mechanic.
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. Obtaining as many passive items as possible means more items to re-roll and more chances for useful synergies.
Getting items from more consistently positive item pools can make a big difference. In particular, Angel Room items and Planetarium items are high-quality on average.
Devil Room items and Curse Room items can be very powerful, but come with the risk of re-rolling into Dead Cat which discards all of Tainted Eden's Red Heart Containers except for one, and those Heart Containers do not return if Dead Cat is re-rolled away later.
The Library can be powerful for Tainted Eden. If Book of Virtues is acquired from a Library, it cannot be re-rolled away due to how Book of Virtues is the only passive item in the Library item pool.
Holding NO! when taking a hit will re-roll Tainted Eden's active item into a passive item, which may or may not be desired.
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.
While "good items" and "bad items" are less of a factor of choice than for other characters since they are frequently re-rolled, there are some that should be of special notice if found or re-rolled into.
Abyss: Can be rerolled, but the locusts are permanent.
Birthright: Prevents items acquired before Birthright was picked up from being re-rolled. This includes normal re-rolls from items like D4 and Missing No., not only the damage-triggered re-rolls.
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 Heart Containers 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 re-roll it into Glowing Hour Glass.
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.
Lil Clot will persist after the trinket is dropped, acting as a semi-permanent familiar until it dies
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 them.
Purgatory: The effect will remain for the current room even if the item itself is re-rolled, providing a helpful boon during boss battles.
Red Stew: The temporary damage boost is retained even after the item is re-rolled, potentially acting as a semi-permanent item effect until the damage boost is lost completely.
The Swarm: The orbital flies granted do not disappear if the item is re-rolled.
Dead Cat: Removes all Red Heart Containers minus one, 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 removed if it is re-rolled away.
Shard of Glass: The bleeding effect from taking damage will still apply even if Shard of Glass is re-rolled, resulting in eventual, constant re-rolls unless Tainted Eden picks up a Red Heart.
TMTRAINER: All items picked up after an item re-rolls into TMTRAINER will become glitched items. Glitched items will not reroll anymore and will frequently be detrimental with their completely random effects. Story progression items also become glitched, which more than likely results in the run ending prematurely.
Brittle Bones: Removes all Red Heart Containers but grants 6 Bone Hearts. Can be very strong if taken early or if low on Red 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.
Chaos: When re-rolled into, any item appearing before Chaos in the item list (that is, older items) will re-roll into items from the correct pool, and items appearing after Chaos (that is, younger items) will be from random item pools. Triggering another re-roll will once again replace all items with those from the correct pool they were in before Chaos shuffled them.
If items are picked up after obtaining Chaos, triggering a re-roll will result in those items being replaced with another item from the pool of the item itself, not from the item pool of where they were obtained (i.e. a Devil Room item taken from a Treasure Room will re-roll into Devil Room items thenceforth).
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 passive to be converted into Soul Hearts that can not be re-rolled.
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 Room item, which should generally be avoided.
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 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.
If Tainted Eden re-rolls while holding two trinkets (such as from Mom's Purse or Belly Button), the trinket in the second slot is dropped rather than re-rolled.
Tainted Eden's transition screen portrait, identical to Eden's.
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.
If Tainted Eden is firing Technology 2 when damage triggers a re-roll, sometimes the laser persists firing in the last-fired direction until leaving the room, even picking up new synergies as other items reroll.
If Tainted Eden is the first tainted character to be unlocked, running out of Eden tokens and selecting "Random" on the tainted character screen will always pick Tainted Jacob.
If the active item is re-rolled into Alabaster Box it will be fully charged instead of discharged as usual.
If Tainted Eden is resurrected during a Co-op game after dying, their graphics will break, cycling between Isaac's head and body.