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Were you looking for the Doomguard ability also called Rain of Fire?

Rain of Fire
Rain of Fire sec cast Y mana Calls down a fiery rain to burn enemies in the area of effect for X Fire damage over 8 seconds.
Usable By
Class	Warlock
Properties
Type	Offensive
School	Fire
Cooldown	None/Global Cooldown
Talents
Improvement Talents	Intensity (warlock talent), Pyroclasm, Cataclysm, Aftermath, Destructive Reach, Emberstorm
Other Information
Ranks	5

This is the rain that falls in the Twisted Nether.

Rain of Fire is the standard warlock Area of Effect spell. Talent points in Intensity increases the chance to avoid interruption when the caster is hit.

Rank	Level	Mana Cost	AoE Damage Dmg over 8 sec	Cost
1	20	295	168	20
2	34	599	384	1  10
3	46	876	620	2  20
4	58	1173	904	4  30
5	69	1480	1212	6  30

Background

Rain of Fire is an arcane spell used by conjurers, mages, sorcerers, wizards, and warlocks. Originally a spell created by the Conjurers of Azeroth, and other casters, it was later used by warlocks.

This is a very powerful spell that combines the natures of flame and water. It calls forth the essence of fire and delivers it through massive thunderheads of vapor and brimstone, creating an actual firestorm. This spell is very destructive, and will cause damage to any foes and buildings in its sphere of influence. Use this spell with care, for the rain of fire knows no friends.^{W1ManH 31} Small meteorites rain from the sky, exploding on impact and burning all in their wake.^{WoWRPG 329} Meteorites deal impact and fire damage to creatures, ignite and batter objects.^{WRPG 165}

Notes

• As an AoE spell, Rain of Fire receives 33% of the bonus from +damage gear. This bonus is then divided amongst the 4 ticks of the spell. For example, if you have +100 damage gear, each tick of Rain of Fire will get +8.3 damage, or +4.2 damage per second.
• Pyroclasm can give add 3.25% chance to stun per second to this spell

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