Tainted Judas starts with 2 black hearts and 3 coins. He does not start with The Book of Belial like Judas does, but instead starts with Dark Arts in his consumable slot. When used, Dark Arts gives Tainted Judas +1.0 speed and makes him invulnerable to damage for a short period of time. Any enemies touched while Dark Arts is active will be frozen until the effect ends, at which point they will take damage (x2.5 your damage + 3.5 flat damage). Any enemy projectiles touched while Dark Arts is active will be destroyed. At the end of the effect, a blast effect occurs. The total explosion damage dealt is proportional to the number of enemies touched, and each enemy killed or projectile destroyed grants Tainted Judas a temporary damage boost. The damage boost scales and lasts longer depending on the number of enemies killed and projectiles destroyed.
Tainted Judas is unable to gain Red Heart. Health Ups will give him Black Heart instead. If he picks up a Bone Heart, he will be unable to fill it with red health.
Tainted Judas is best suited to a highly aggressive playstyle; making effective use of Dark Arts by rushing into the fray and striking as many enemies as possible, then clearing up stragglers with buffed damage. However, it shouldn't be mistaken as a purely offensive tool, as the ability to destroy projectiles gives it great defensive utility when used properly. For example, timing its activation to cross through the origin point of a nova of bullets as they spawn simultaneously removes the need to dodge and grants a massive damage boost.
It is vital to get a feel for how long Dark Arts remains active, as being inside an enemy or hazard when it ends will typically result in damage taken.
Dark Arts can nullify a lot of the harder puzzle rooms, as one can walk straight through spikes and shots while it's active. In addition, being able to safely enter Curse Rooms grants a risk-free opportunity to build up soul/black hearts or find powerful items every floor.
Certain enemies or bosses that rapidly fire bullets, such as Soy Creeps, Revenants, Baby Plum, Hush, etc. are a boon for Tainted Judas; as every bullet walked through contributes to the damage bonus, these can stack up extremely quickly, and as long as the enemy/boss remains alive, this can be repeated indefinitely. This can lead to obscene amounts of damage that can potentially last through an entire run.
Tainted Judas is extremely effective in Greed Mode, due to the ability to wholly ignore damage from Curse Rooms / spikes inside the store and the quick transitions between waves allowing for repeated use of Dark Arts to continue stacking damage.
Dark Arts can also be used to ignore the damage from the button and pause the timer for free.
Due to his similar health system, many of the benefits that apply to ??? in regards to health can be applied to Tainted Judas as well.
Items that rely on being in close proximity to enemies can be extremely beneficial, due to how often you will need to sprint through them to build Dark Arts effects.
Ipecac is extraordinarily effective with Dark Arts, as the damage of the Dark Arts hits scales off of the Damage stat, which is increased significantly by Ipecac — it becomes possible to easily shred bosses in a single hit, especially if multiple projectiles are tagged beforehand. However, due to Tainted Judas' low base range, it is easier to hit yourself.
As Dark Arts encourages a risky playstyle of throwing oneself into swarms of bullets, items that can block damage while Dark Arts is inactive (such as Host Hat, Infamy, Holy Mantle, and Belly Jelly) are very effective.
Dead Eye has incredible synergy with Dark Arts, as their damage ups combine together, and Dark Arts can never "miss". This allows Tainted Judas to gain a massive damage boost from one cast of Dark Arts, provided he hits enough valid targets with it.
False PHD: The play style of Tainted Judas makes his tear stats (like shot speed, range) less important than other characters, so a damage up can be more beneficial than other stats (except speed) down. False PHD can also gives Tainted Judas black hearts.
Saturnus: Allows for "firing" while using Dark Arts, as well as safer collection of enemy tears.
Hungry Soul: Due to how quickly Dark Arts kills weak enemies, the chances of souls appearing can be multiplied.
The decision to use projectile-destroying items (Halo of Flies, Psy Fly, etc.) is one that will need to be judged from playthrough to playthrough. For newer players or during a poor run where damage to oneself needs to be minimized, they are very useful during the downtime between Dark Arts activations. However, for more experienced players or during runs where soul/black hearts are plentiful, they can prove to be quite detrimental as they will block projectiles before Tainted Judas touches them, lowering the Dark Arts damage buff.
Orbitals that deal high contact damage (such as Cube of Meat or Sacrificial Dagger) work well with Dark Arts, as they deal substantial damage while passing through enemy hitboxes, often enough to negate the damage lost from nullified projectiles. However, enemies killed through means other than Dark Arts will not contribute to its damage bonus.
Depending on a player's skill level, items that reduce the size of the character's hitbox (Such as Binky, Mini Mush, and the "One makes you small" pill) may start to become less desirable picks, as they can sometimes make bullets and enemies harder to hit.
Shade will increase your damage output with Dark Arts, whether it’s been absorbed or not. When it hasn’t been absorbed, it may cause some confusion as to which character you are controlling, as it looks quite similar to Tainted Judas at a glance.
With The Ludovico Technique, the tear remains in the air when using Dark Arts, allowing you to deal damage while it floats. With precise movement, you can position your tear on enemies and attack them with Dark arts. This leads to large damage with other Ludovico synergies, as without them it means less use out of the damage up from Dark Arts
Due to his similar health system, many of the detriments that apply to ??? in regards to health can be applied to Tainted Judas as well.
Dead Cat takes away all your black and soul hearts except for one.
Libra should be avoided. The stat-equalizing effect is constantly active, and this weakens Dark Arts in two major ways:
It siphons most of the Speed increase during Dark Arts' activation into other stats, most of which are useless as they only benefit tears.
Once Dark Arts ends, the damage buff is instead fragmented into various negligible stat bonuses that fall off far too rapidly to be properly utilized.
In the same breath, Zodiac is also recommended to be avoided as it might just give you Libra at the worst possible time.
Lost Soul doesn't go invincible when Dark Arts is used, so it is guaranteed to die because of how Tainted Judas is meant to be played, and thus will never pay out — making it useless.
Broken Modem: May remove shots or change the pattern enemies are moving in, resulting in a damage loss.
Finger! / Pointy Rib: If the player's damage is too high, you may not be able to get to enemies before the damage from the finger or rib kills them.
The achievement for unlocking Tainted Judas, "The Deceiver", may be reference to Judas Iscariot, the disciple who betrayed Jesus Christ, it may also be a reference to the Judas Priest song "Deceiver".
This is also one of the meanings of his card, I - The Magician?, associated with manipulation and trickery.
The assassin-type design of Tainted Judas, together with the Dark Arts he holds, might be inspired by a (not widely accepted) theory considering that the biblical Judas Iscariot belongs to the Sicarii, a group of Jewish cloak-and-dagger assassins who strongly opposed the Roman occupation of Judea.
The Sicarii, named after the word "Sicarius" which means dagger-wielder, are regarded as one of the earliest known organized assassination units of cloak and daggers. Sicarii were known to attack Romans and Roman sympathizers alike with daggers hidden in their cloak, then blending into the crowd after the deed to escape detection. The playstyle of Tainted Judas bears strong resemblance to this, while the sprite of Dark Arts can be a further evidence.
Tainted Judas uses a modified version of Dark Judas's sprites, with the only difference being an additional costume that consists solely of the red cross brand and fez.
Dark Arts is Dark Judas' starting item in The Binding of Isaac: Four Souls. As expected, the card and the item have entirely different effects.
Ceremonial Blade is Tainted Judas' starting item instead of Dark Arts.
The description of the unlockable Soul of Judas may be a reference to Meet the Spy, in which the spy says, "Right behind you"
Tainted Judas's transition screen portrait.
Tainted Judas's locked character icon, depicting a closet door with a knife sticking out of it.
Tainted Judas in his Dark Arts state can be affected by Pause, this results in Tainted Judas being stuck in his shadow form whilst not being able to fire any tears as long as Pause is still in effect, this can be fixed by quitting then entering the game again.