Wikia

Immortal Guardians are faceless ones that spawns during the Yogg-Saron encounter in Ulduar.

Attacks and abilities

Melee for ~20-25k on plate to start with full empowered stacks.

[Empowered]^ω ϖ—Empowers an Immortal Guardian, increasing the damage it deals when its health value is high. Damage increased by 180% per stack. Begins at 9 stacks. Every 10% HP the Immortal Guardian loses/gains will remove/add a stack.
[Shadow Beacon]^ω ϖ—The Immortal Guardian becomes a beacon for Yogg-Saron's Empowering Shadows. It will receive the buff after 10 seconds.
Immortal - Immortal Guardians cannot be slain except by Titanic Storm while at 1% HP.

[Drain Life]^ω ϖ (channeled)—Transfers 2,000 health every 1 sec from the target to the caster. Lasts 5 sec.

[Drain Life]^ω ϖ (channeled)—Transfers 3,333 health every 1 sec from the target to the caster. Lasts 5 sec.

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Patch 3.2.0 (04-Aug-2009):
- An Immortal Guardian targeted for Empowering Shadows in the Yogg-Saron encounter will now become a 'Marked Immortal Guardian' while targeted.
- Empowering Shadows in the Yogg-Saron encounter now targets a maximum of three Immortal Guardians in 25-player mode.
Hotfix (2009-06-30): "Immortal Guardians are now able to target players in the "illusion room" of Yogg-Saron with their summoning ability."
Hotfix (2009-06-30): "We're also in the process of deploying a hotfix for an issue with Immortal Guardians that could cause them to pause their movement before reaching melee range. This fix will also prevent the Immortal Guardian from running away if their target is stunned."
Hotfix (2009-04-21): "The Yogg-Saron encounter has received the following changes: Guardians of Yogg-Saron in phase 1 and Immortal Guardians in phase 3 have had their health reduced by 15% in heroic mode, the Destabilization Matrix cast by Mimiron will now correctly hinder the casting speed of Crusher Tentacles in both normal and heroic modes."
Patch 3.1.0 (14-Apr-2009): Added.