Temporarily transform into a demon, increasing damage dealt by 24.00%. Metamorphosis prevents the use of Corruption and Hand of Gul'dan.
A warlock in demon form
Metamorphosis is a warlock ability learned at level 10 for those with the Demonology specialization. It is the hallmark of that specialization, allowing use of a demonic form powered by Demonic Fury, granting an array of unique abilities.
While shapeshifted, the demon-form warlock can be banished. Demon form is also susceptible to Turn Evil and grants an auto-crit on Exorcism but is immune to enslave demon.
Also you speak Demonic instead of your normal language.
Metamorphosis can be used for AoEFarming by picking up a bunch of Mobs and then using Immolation Aura and Hellfire
Trivia
Metamorphosis is adapted from the iconic demon hunter ability of the same name, and is visually based on Illidan Stormrage's demon form.
Metamorphosis is considered [form:2] in macros.
At one point, warlocks in demon form could be enslaved.
Patch changes
/Patch 4.0.1 (12-Oct-2010): Challenging Howl, Shadow Cleave, and Demonic Charge Removed, Replaced with Demon Leap.