The Heretic

The Heretic is a boss added in The Binding of Isaac: Repentance that can appear in.

Phase 1

 * During the beginning of the fight, 5 Exorcists, which are shielded and invulnerable, summon The Heretic from a large pentagram after which they turn into Fanatics.
 * The Heretic is incorporeal until all Fanatics and the Pacers or Gushers they turn into are dead, similar to The Haunt's first phase.
 * While incorporeal The Heretic can still do contact damage.

Phase 2

 * Lobs 7 projectiles that, after landing, burst into 6 fires that spread out in a radial pattern. The landing position of each projectile is marked on the ground.
 * The Heretic then follows up by launching itself towards Isaac creating a radial burst of 8 lines of fire where it lands. It spends a short time readjusting its dislocated jaw before continuing to attack.
 * The arena of the Heretic always spawns a number of unlit Fire Places. The Heretic can light up 5-6 of them before firing a laser that connects all of the lit fires. The order the Heretic lights each fire indicates what order the laser travels.
 * These can be extinguished with an explosion, preventing Brimstone lasers from reaching the deactivated Fire Place.
 * Dashes off-screen and turns invisible before charging in again, predicting Isaac's movements and attempting to bite down on where Isaac is moving, doing a full heart of damage if the attack connects. It chains this attack a total of 4 times, each time from alternating sides of the room.
 * The Heretic occasionally does not finish the fourth charge, instead fading away and quickly charging in one final time from the other side of the screen.
 * Upon death, the Heretic's fiery eye drops down and sends out lines of fire in the cardinal directions.

Trivia

 * It appears to be a resurrected variation of The Haunt or The Forsaken.
 * The Exorcists that appear during the beginning of the fight to summon The Heretic are found nowhere else in, unlike in Antibirth where they were a regularly appearing Monster.
 * As of Repentance version 4.0.3, the Exorcists exist in the bestiary, but even using a to kill them will not add them to the bestiary, leaving it currently impossible to complete.