|First phase: 35 per cultist|
Second phase: 789
The Heretic will always have an arena filled with extinguished campfires, which he uses for one of his attacks.
At the beginning of the fight, five Fanatics will be gathered around a pentagram circle. They are invulnerable until The Heretic appears. When The Heretic spawns, he will be invulnerable to damage similar to The Haunt's first phase until all the Fanatics have been killed. The Fanatics walk towards Isaac to deal contact damage, occasionally firing homing tears.
The second phase has The Heretic coming out of his invulnerability to attack Isaac. He has three attacks:
- The Heretic will point to extinguished fireplaces, lighting them up one by one as Purple Fireplaces. Once several have been lit, The Heretic will fire a brimstone beam, hitting the fireplaces that connects them in the order of lighting (Fire 1 will connect to Fire 2, Fire 2 to 3, etc.)
- The Heretic will vanish, and appear either to the left or right of Isaac, and will charge and attempt to bite Isaac, homing slightly. He repeats the process four times, alternating which side he charges from.
- The Heretic will start lobbing purple tears at the ground that splash into a ring of six fires that spread and vanish after a certain distance. He does this several times, and ends it by moving above Isaac's position and slamming into the ground, spreading lines of purple fire in eight directions.
- Upon death, he will release lines of purple fire in the cardinal directions.
- The fires can be extinguished as he's pointing at them using bombs or other explosives, which reduces the area of the beam's coverage.