The imp is a common PVP pet because of its buffs but can usually be ignored. Its damage can usually be negated with Pet Forest a fire ward and if their master is soul linked it will die on its own. 

A void walker is another pet that can be ignored. Its only real threat is the way its auto attack can push back your spells and that it can be sacrificed for a damage shield. But if you time it right you can spell-steal that shield from the warlock and use it for yourself. A succubus is a dangerous pet because of it does seduce ability.

If she manages to land it you will be out of control and the warlock can attack you with impunity, so try to burst her down with instant casts. A felgaurd is another dangerous pet because of its intercept ability. Since it is melee you can trap it with freeze effects more easily than with the succubus, but you still need to take it down fast.

The absolute worst pet a warlock can throw against you is the felhunter. Its two strongest attacks are its silence and it’s dispel. Stick to instant and fast casting spells to avoid spell lock as much as possible.

Its dispel is also dangerous because it will Pet Forest Gold eat any magical debuffs on itself or its master. This makes Ccing the warlock very hard, especially polymorph.