Warlock's Felhunter Pets

At level 30 you get the Felhunter. The Felhunter is very useful against other casters, using spell lock, which interrupts an enemy caster's spell, and--for six seconds--prevents the caster from casting any spell from the same class of magic. The felhunter's "Devour Magic" ability removes negative magic on you (or positive magic on an enemy) and heals the felhunter every time he performs it. The felhunter is the PVP pet of choice yet lacks in PVE due to threat generation, it is best to use the voidwalker when not playing in a group.

Don't discount him as a tank pet, either. His Tainted Blood ability reduces attacker's power significantly if you let him take a few hits before you enter the fray. This in combination with Curse of Weakness can keep your Felhunter from taking much damage at all.

Careful threat management can make fighting with the Felhunter smooth and painless. Send the Felhunter in to attack, and watch the mob's health bar. As soon as the Felhunter hits the enemy for the first time, cast Curse of Weakness -- this will not cause enough threat to draw the mob away. Wait until the mob's health bar has decreased visibly by a tick, then cast Corruption (and Siphon Life if you have it). You may want to use Life Tap at this point to recoup the mana you have used.

Wait until the mob's health has decreased a significant fraction -- experiment with different enemies and see how this varies. Then use further attacks, such as Immolate, Shadow Bolt, your wand if you have one, or perhaps even a direct melee weapon attack. You can also use Drain Life to restore the health you lost by using Life Tap. If the mob does turn away from your Felhunter to attack you, don't panic; just cool it for a moment, stop attacking, and it'll go back. At this point some of your DoTs may be wearing off; you can judge whether and when to put them back based on how easy it is to draw the threat back onto you. It takes finesse, but you can usually dispatch enemies your level and come out with almost full health and mana. Your Felhunter may be a little worse for the wear, but pets recover very quickly.