The Demon Form abilities are the following:
- Challenging Howl (Instant, 15 sec cooldown): Taunts all enemies within 10 yards for 6 sec.
- Demon Charge (Instant, 45 sec cooldown): Charge an enemy, stunning it for 3 sec.
- Immolation Aura (Instant, 30 sec cooldown): Ignites the area surrounds you, causing X Fire damage to all nearby enemies every 1 sec. Lasts 15 sec. Spell power coefficients: 243.23% total (~214.5% before the 20% damage bonus), 16.22% per tick (~14.3% before the damage bonus). Damage also increases based on level.
- Shadow Cleave (Next melee, 6 sec cooldown): Inflicts 110 Shadow damage to an enemy target and nearby allies, affecting up to 3 targets. Spell power coefficient: ~25.6% (~21.3% before the 20% damage bonus).
Also you speak Demonic instead of your normal language.
In PvP, it's only advisable when fighting in a one-on-one situation (primarily against Rogues), as in a brawl, a big, black and horned demon is the favorite target for everyone.
Of course, Metamorphosis can also be used as a flat damage boost for 30 seconds.
An interesting fact you should notice about this is it reduces your chance to be critically hit by 6%, which is just above what you need to be uncritable by a raid boss. Coupled with the 600% armor increase and taunt it makes this an option for lock tanking bosses that primarily use spells. The lack of avoidance enhancements in addition to the fact that demon form only lasts for 30 seconds makes it somewhat dangerous to tank very hard and fast-hitting melee bosses. This can be useful against the Blood Prince Council as a range tank.
The demon form does use a model extremely similar to Illidan's from the Black Temple.
- Metamorphosis is considered [form:2] in macros.
- At one point, warlocks in demon form could be enslaved.