The Codex of Xerrath (ability)

The Codex of Xerrath is a passive warlock ability learned by defeating Kanrethad Ebonlocke and completing the Pursuing the Black Harvest scenario, which corrupts all of the warlock's fire spells with fel magic, giving them a green, entropic fire effect. Icons, spell effects, and UI elements are all affected. It also alters the appearance of Metamorphosis (warlock ability), causing it to resemble Kanrethad's green demon form.

The ability can be unlearned by speaking to Jubeka Shadowbreaker in Shadowmoon Valley after completing the quest, for. It can be relearned by clicking on Kanrethad's banished form, located atop a nearby hill.

• Rain of Fire
• Burning Rush
• Metamorphosis (warlock ability)
• Hellfire
• Wild Imps
• Immolate
• Ember Tap
• Conflagrate
• Incinerate
• Flames of Xoroth
• Metamorphosis (warlock ability): Immolation Aura (warlock ability)
• Soul Fire
• Felsteed (mount)
• Dreadsteed
• Summon Abyssal
• Demonic Fury
• Dark Apotheosis
• Demonic Leap

In addition, Chaos Bolt, which is green to begin with, becomes larger and resembles Kanrethad's empowered version.

Also for Destruction Warlocks, the Burning Embers UI graphic turns green.

The ability can be unlocked by defeating Kanrethad Ebonlocke at the end of the Pursuing the Black Harvest scenario. (see Kanrethad Ebonlocke (tactics) for further details). Once unlocked it can be toggled on and off at The Hand of Gul'dan.

Once the ability is unlocked, it can be turned on by siphoning fel magic of a banished Kanrethad at the Altar of Damnation near the Hand of Gul'dan at Shadowmoon Valley.

To turn off the effect, speak to Jubeka Shadowbreaker who is also at the Altar of Damnation and ask her to remove the fel corruption. This will return your fire spells to their default color.