Dark Arts

Dark Arts is an activated item added in The Binding of Isaac: Repentance. starts every run with this item in his consumable slot.

Effects

 * When used, Isaac gains +1.0 speed and can walk through enemies/bullets for 1 second or until he shoots. If Isaac walks through an enemy or bullet during this time, it freezes until the effect ends, then takes damage equal to 2x Isaac's damage plus a flat 3.5. If there are multiple enemies/projectiles caught in the attack, each consecutive attack deals an additional flat 3.5 damage. At the end of the effect, an area of effect blast is created, dealing more damage the more enemies or bullets were pierced during the effect.
 * For every enemy/bullet Isaac walked through, he will gain a temporary +1 damage bonus, which wears off at a rate of -0.25 damage every half second.
 * The damage of the blast at the end of Dark Arts is equal to the sum of every damage dealt while dashing between enemies.
 * Bullets walked through will still count for the final blast damage calculation, even though they can't really be damaged.

Synergies

 * : Mom's Knife will still deal damage even while in Dark Arts, killing most weaker enemies and bosses easily.
 * : Jumping over an enemy or projectile while Dark Arts is active will tag it.
 * : Kamikaze! can be activated without harm when using Dark Arts.
 * : Activating Dark Arts will not cancel the effect, turning Pause into an instant room clear in most situations and an effective tool for damaging bosses, allowing you to get up to 4 uses in before they resume.
 * + : Pause becomes an even more effective tool against bosses, as it can now be activated several times in the fight.
 * + : Pause can be used every room, making most of them very easy to clear
 * : The corns created by Montezuma's Revenge can be caught by Dark Arts, and most will naturally, making each cast of Dark Arts give huge boosts of tear damage, and making the final blast deal huge amounts of damage. Also, the Brimstone beam created will still be active while Dark Arts is active.
 * : Isaac is able to dash while using Dark Arts, allowing him to reach more enemies in one use of Dark Arts while still dealing damage with Mars' dash.
 * : 120 Volt will still activate while using Dark Arts, allowing Isaac to deal more damage to nearby enemies while invulnerable.
 * : Will be activated during the usage of Dark Arts, activating the invincibility in the same instant that Dark Arts is activated.
 * : If Isaac is stationary when Dark Arts ends, he will gain invulnerability without any downtime. Dark Arts can also be used from invulnerability without taking damage.
 * : Due to the nature of Dark Arts, Isaac can easily damage enemies with the trail left behind.
 * : Rock Bottom will prevent your damage from decreasing, allowing you to keep the highest achieved damage bonus.
 * : Dark Arts will last twice as long, totaling at 2 seconds per use. If you end Dark Arts early, a second Dark Arts will activate for the time that you had remaining.
 * : If used at the start of a room, after Dark Arts' effect ends, Isaac re-enters Stealth.
 * Wisps: Wisps cannot be destroyed while Dark Arts is in effect and still deal contact damage.
 * : Because Dark Arts' damage is scaled off of tear damage, Ipecac gives an extremely high damage boost to each Dark Arts hit, easily capable of destroying some early bosses in a single hit.
 * : When Dark Arts ends, each enemy tagged may instantly die and release a burst of black tears as if hit by a Euthanasia tear.
 * : Dark Arts can be used on friendly mobs created by Friend Finder without killing them, but still giving you the damage boost.
 * Enemies which spawn other enemies can be captured and used to generate infinite damage, as the enemies they spawn will also be friendly.

Interactions

 * : Libra is extremely detrimental to how Dark Arts works, and should be avoided: The speed boost during the invincibility phase is transferred into attack bonuses (Which are useless as tears cannot be used), and afterwards, the temporary damage boost is divided across all of Isaac's stats, resulting in very negligible stat boosts.
 * Familiars such as that block projectiles will make it difficult to gain damage off of projectiles, as they destroy any projectiles they come in contact with.
 * Clots: Clots will gain increased speed and be no longer be able to fire, but will still be vulnerable to damage while Isaac is using Dark Arts. They will most likely hit any enemies or projectiles Isaac runs through if the player does not use the drop button to make them stay still.
 * Using while there are enemies and also tagging the White Fire Place will extinguish it.

Trivia
The item is a reference to a flash game Edmund Mcmillen created in 2005 called Grey-Matter. In this game, you would kill enemies in a fashion identical to Dark Arts.