Heretical Monster
The Heretical Monster (in-game name Kerettiläinenhirviö) is a diamond-shaped boss encountered in the Temple of Sacrilegious Remains. It has a variety of attacks which inflict dangerous debuffs on the player. In order to awaken the boss from the temple, the player must collect an Orb of True Knowledge to lure it out, shortly afterwards the fight will begin.
Behaviour & Combat
After appearing, the Heretical Monster has a variety of attacks it will use.
Frequently, the boss will cast a barrage of large spectral wands and shoot a barrage of Shadowy Beams out of each one.
Upon taking damage, the boss can retaliate by firing 1-2 random master orbs towards the player, inflicting a large array of debuffs on hit.
Periodically, the Heretical Monster will summon minions to help it in battle, who will try to cast master orbs of their orb towards the player.
Additionally, the boss will periodically begin creating a ring of purple sparks around itself alongside a vacuuming sound effect, a few seconds afterwards, the boss will release a large barrage of Wand-Stealing Master Orbs alongside casting multiple explosive projectiles in a cross formation that will break nearby terrain.
It is recommended to take cover and hold an item opposed to a wand during this period, as wands can not be stolen if the player does not have one equipped.
The Heretical Monster will also occasionally inflict 
Wounded on all nearby creatures, including the player, this will disable healing for the player temporarily, requiring them to time their heals appropriately.
Phase 2
After reaching 40% health, the glyphs on the boss will light up, caution should be exercised when this happens as it will summon a ring of Alkeeminen Outos, which inflict various material hex debuffs when damaged.
Additionally the boss will now cast Mass Lively Hex instead of Mass Wounding, inflicting 
Lively Hex on all nearby creatures, including the player, for a short duration, making the player take %health damage from touching bloody substances.
Phase 3
Phase 3 occurs after the boss reaches 10% health, initially the boss will immediately begin creating a ring of purple sparks around itself to prepare for another purple orb barrage as well as summon more Alkeeminen Outos alongside Korruptoitunut Sätkymestari in an attempt to lure the player into attacking the previously summoned Wraiths.
The boss will also begin to move faster, making it difficult to avoid without tools to increase the player's movement speed.
Phase 4
Phase 4 occurs after the boss initially dies, rather than dying outright, the Heretical Monster will instead loose it's armor and continue fighting.
During this phase, the boss stops casting Mass lively Hex and instead reverts to casts Mass Wounding, inflicting Wounded periodically and disabling the player's healing.
The spectral wand barrage now fires 3 wands simultaneously rather than over time and instead of retaliating with master orbs, the Heretical Monster will periodically shoot a spread of orbs, which inflict Lively Hex, causing the player to take %health damage from bloody materials.
Rewards
- Full Health Regeneration
- Extra Max Health
- Korruptoitunutkivi
- Heretical Eye
- Unlocks the Alt Fire Targetter and Hemomancy spells to appear in future runs
- Additionally, on the hardcore and nightcore seeds, the boss will drop the Copy Spells perk, allowing the player to copy previously uncopyable spells
Tips
- Despite Corrupt Masters of Grounding disabling the player's plasma shields periodically, Permanent Shield makes the fight much safer against stray master orbs
- Kerettiläinenhirviö can be seen above the Temple of Sacrilegious Remains orb room before the player encounters it.
- The Targetter spell may be ideal against this boss, as it can turn the Heretic's minions against itself
Trivia
- The boss has various glyphs on it's body, spelling out different phrases