World of Warcraft®

You restore 20% of your total health after you kill a target in Demon Form that yields experience or honor.

Teaches you the ability Imp Swarm.
Requires Demonology.

Imp Swarm
Summons 5 Wild Imps from the Twisting Nether to attack the target.

The Wild Imps passive effect is disabled while Imp Swarm is on cooldown. Imp Swarm's cooldown is reduced by spell haste. Also increases Wild Imp's cooldown by 4 sec.

Requires Demonology.

Teaches you the ability Dark Apotheosis.

Dark Apotheosis
You imbue yourself with demonic energies, reducing physical damage taken by 13.85%, reduces magic damage taken by 15%, and allows the use of various demonic abilities.

In addition, Soulshatter becomes Provocation which taunts your target, Twilight Ward becomes Fury Ward which will absorb all schools of damage and Shadow Bolt becomes Demonic Slash.

Your Hand of Gul'dan can now be targeted at a location.

Your Felguard will equip a random two-handed axe, sword or polearm from your backpack.

Your Felsteed and Dreadsteed can cross water while running and leave a trail of flames.