One of the most important decisions is which pet to use, and how to use it:
Imp
Especially if boosted with Improved imp, Improved Firebolt and Unholy Frenzy, he is a chaingun. But, because he runs out of mana (and health) swiftly, you can only rely on him to output meaningful damage for a short while. Even if you had Mana Feed, you wouldnt want to be lifetapping in a hurry in PvP. In a 1 on 1 situation the imp can be an option if you manage to take out the enemy quickly, but he is generally not the best choice. The imp’s phase shift spell means it cannot be damaged unless it attacks something, so you can keep it around and have it attack when it best suits you. In mass PvP situations, you could choose to keep him in phase shifted form most of the time, buffing your group with blood pact and fire shield. If you have it, use Dark Pact on him to refill your mana.
Voidwalker
This pet completely loses his tank functionality in PvP. No one in his right mind will focus on trying to damage a voidwalker instead of a player. However, he does have a place in PvP thanks to his Sacrifice ability, and is especially good if you have the Master Demonolist and Soul Link talents. Sacrifice allows you to cast spells without interruption, letting you absorb some damage and get one or more cast time spells off easily. Secondly, he does do a little bit of damage, and can be used to annoy spellcasters until you need to sacrifice him.

Succubus
This pet is pretty nice for PvP. She has two critical abilities that make this so. For one, invisibility makes her undetectable by your enemies. A warlock without a pet appears to many as an easy target. (Although experienced PvP’ers will expect a succubus if none is visible. But usually cant do much about it.) Bear in mind that other warlocks can see her, provided they bothered to cast detect invis.
Now, the complementing ability is Seduce. An important note regarding seduce in PvP here: Seduce shares diminishing returns with Fear. This means that subsequent casts make the spells less effective, up to 15 second immuny to both after 3 casts.
I emphasize that seduce and fear share these diminishing returns. Casting fear on a target three times will make the target immune to both fear and seduce.
These diminishing returns do not apply in PvE fights.
Now, what can you do with the limited seduce opportunities you have;
Seduce - Nuke – Seduce
As simple as it looks. Seduce your target, and cast a shadowbolt. Let your succubus start recasting seduce before your bolt hits the target. If you time it just right, your nuke will hit, and the target will be re-seduced right after. A good thing to know is that letting your pet cast seduce while she is invisible will not break her invis until she finishes the spell. This makes for a deadly combo of abilities. This strategy has gotten into disuse every since fear and seduce share cooldown. It still has its use at times though, especially if you have a lot of +spell damage.
Seduce – DoT – Fear
Seduce does not wear off until the target takes damage, or the spell timer runs out. Corruption, Curse of Agony, Unstable Affliction and Siphon Life don’t deal any damage the moment they land on a target. They deal their initial damage 3 seconds after landing. Using this to your advantage, you can seduce a target, apply corruption, curse of agony and immolate, and then fear right after. The downside is that this uses up two of the 3 successive casts of either fear or seduce before 15 second immunity occurs.
It can also be used to interrupt a spellcaster, provided seduce actually lands in time, before they finish their spell.

Felhunter
Very useful in PvP. Using devour magic and spell lock he is particularly effective against caster types. They usually aren’t too pleased to see their polymorph or heal spell cancelled mid-cast, and then find they can’t cast any spell of the same school for the coming 8 seconds. The Felhunter can use devour to remove DoTs and debuffs from you, or be used on the enemy to remove their buffs, heal over times, and timed effects.
Felguard
The Felguard is an excellent PvP pet. Combining high damage output with the short stun from intercept, he makes for a big distraction to the enemy. His AE avoidance makes things like priest fear, frost nova and the like be avoided frequently. While he lacks an ability comparable to Seduce, Sacrifice or Devour, he is still a very welcome addition to the arsenal of the PvPing demo lock.
Enslaved demons
Enslaved demons have their place in PvP, although the Doomguard is rarely, if ever, seen due to its difficult summon process. The Infernal however, is used more frequently.
Infernal
The Infernal has a few things going for it:
·You can summon it at will (Once every hour, that is) and its enslaved right off the bat for the guaranteed 5 minutes. That’s enough in PvP.
·It has a decent amount of hitpoints, does good melee damage, and is immune to fire damage.
·Its AE damage will delay enemy spellcasting (like any damage does).
·It has a high Big and Scary factor.
Banish is the bane of this pet, although having a banished one sitting on a friendly flag will make it pretty hard for the enemy to capture. Its ae carries on while banished, and interrupts them.

Doomguard
The Doomguard would be a great pet to use in PvP, if it werent for some problems. The main problem is the difficulty of actually summoning a Doomguard. Getting 5 people to help you is tough at best, especially if one will die. You can try ritual of doom to get it, if theres mobs to kill in the surroundings. Doing that can take a lot of time, while you may die quite rapidly in PvP when you finally have it. Another downside is the need to enslave it before it kills you off. The worst thing is that it can simply be banished, and thus become absolutely useless.
Should you manage to get one, its quite good. Cripple slows enemy movement speed to 60% of normal. If you have it, supplement with curse of exhaustion for extra effect. Cripple also slows attack speed by 30%, which is significant. War Stomp can interrupt enemy spellcasters, and will allow you to get off a Howl of Terror without interruption. Rain of fire can do a great deal of damage if enemies are bunched together. Add your own RoF or Hellfire for extra damage. Sadly, the Doomguard serves as a beacon. People want to kill it, because its big. A one hour cooldown minor distraction, meh.