The vast amount of mass PvP happens in the battlegrounds, although outdoor pvp objectives are going to be added soon.
When you are part of a force, fighting a force, you will play much differently than if it were one on one. This especially holds true for Battlegrounds, where the objective will often require you to capture and protect something, or accomplish a goal that doesn’t revolve around killing as many opponents as you can at random.
Most of the time, raids aren’t this organized or disciplined, and people often go out on their own to get honor kills. It’s a shame, but that’s what 90% of the BG’s are like.
When you are lucky enough to be in a BG with some form of organization, which you usually find in one or more guilds working together, you are likely to get much more intensive and exciting fights. Working together effectively against the opposing faction and completing a BG is a good fun.
Some General Mass PvP Tips:
●In large fights, you can create a disorder by using Fear and Howl of Terror. It disorients people, and puts them out of the fight. Even if it only works for a short time, this is a big plus.
●You have a large chance to be singled out as a target when you stray from the group, so dont wander about by yourself too much.
●The Infernal can serve as a decent distraction. People have a tendency to attack the big target, which keeps them off of your allies, for as long as it survives. If there are warlocks around though, it tends to just get banished a lot.
●AE! These are by far the best way to damage a large amount of players. The more chaotic the fight, the better. You have a lower chance to be spotted that way. Seed of Corruption is very nice when people are clumped together, and often it isnt dispelled. Since hellfire centers around you, you have a larger chance to get spotted casting that than you do with rain of fire. Judge for yourself whether its

worth the risk, it depends completely on the situation. If you have the intensity talent, it’s of good use when AEing in PvP.
●Have nightfall? Siphon life? Casting corruption (You can use level 1 to save mana) on multiple targets will greatly increase the chances of nightfall activating. Casting siphon life on multiple targets will give you very respectable life regeneration for a while, unless the opposing forces are quick to dispel.
●If you have Dark Pact, and the fights are drawn out (not uncommon in Alterac Valley), you can use it to replenish your mana while fighting.
●Use Eye of Killrog to scout out the enemy in relative safety.
Battleground Specific Tips
As every Battleground has it’s own objectives, the way a fight goes can differ wildly from zone to zone.
If you die in a Battleground your pet will come back to you when you resurrect, saving time, mana, and a soulshard. If your pet was an enslaved demon, Infernal or Doomguard when you died, you will resurrect with an Imp.
There is a bug where you will sometimes respawn with no pet.
You can kill yourself with lifetap+hellfire and get resurrected again to get your pet, if need be.
Anothr peculiarity is that the game ignores the pet you first enter the BG with. Whether you zone in withg a succubus, voidwalker, felhunter or imp doesn’t matter, your first death will always be rewarded with an imp. Only after summoning a pet inside the instance will it be ‘saved’.
Warsong Gulch
A simple and small zone. The objective is to capture the enemy flag, and bring it back to your base. A good raid force will make their capture attempts as a joint force, using a variety of class, but most importantly healers to protect the flag carrier. To break such a train, the flag carrier must be slowed, and the healers taken out. All too often the flag carrier is attacked directly, which essentially is an attack to the healers mana bars, and a bad idea, as they’ll last long enough to reach the other side of the zone. Causing a moderate amounty of chaos by using Howl of Fear can be helpful, if you can manage to get the spell off.

Focus on killing the healers. Fear them. CoEx the flag carrier if you have it. Even if its dispelled quickly, it will still slow them for a moment. Spell lock a healer. Death Coil! Anything you can do to stall the flag carrier and kill his support.
If you are part of the assault force, try to scout out the enemy base with an Eye before the attack is made. If you should find a spot inside their base to hide in, that is even better. You can keep close tabs on whats going on that way, and relay the info to your raid, making it easier to pick the right moment for attack. Note that seeing no one in the enemy flag room often means that there are often people on the roof, high above, ready to jump down. There may be stealthed rogues about. Lastly, there is usually a hunter frost trap by their flag. It can be set off by anyone, and be dispelled as well, so it should not be a big problem.
Once the flag is captured, protecting your flag carrier as he’s on his way back to the base becomes essential. Using Howl of Fear and regular Fear on the enemy can make a huge difference here. If you have CoEx, it really shines here. Cast it on every enemy you see trailing your flag carrier. Use seduce too, should you have a Succubus out. Or help keep your flag carrier clear of any snare / root effects that can be devoured with Felhunter.
Arathi Basin
This is a medium sized battleground, the objective is to capture and hold as many of the 5 different buildings possible. As you hold the buildings, points will start flowing in. The first team to reach 2000 points wins. Protecting the flags you capture is instrumental to victory.
Most people don't like guarding flags, and this knowledge can be used both defensively (by guarding a flag yourself) and offensively, by taking over poorly defended enemy flags.
This battleground can not last long than a certain time, because there is always a team that controls a given amount of buildings, and the points keep trickling in.
Tip: Cast an infernal on a flag people are trying to steal from your team.
Alterac Valley
This is a large battleground, and will often last for many hours before either side wins, if a victory on either side occurs at all. Because of its scale, and the amount of people involved, progress is made slowly. Should your raid force be clearly superior to the enemy, then a win can happen.

There is nothing really specific to do for a Warlock, unlike in Warsong. Following the raid direction, if there is any, completing objectives and gaining faction is the main thing you can do in here.
Howl of terror comes in handy if you wish to capture an unguarded graveyard here. Rain of Fire is good for interrupting mulitple enemy flag capturers.
The Eye of the Storm
This battleground was introduced with The Burning Crusade. It is a mix of Arathi Basin and Warsong Gulch. There are both flagged buildings and a flag in the center. The buildings are captured by simply standing near them, similar to the world pvp objectives in Outland. As you control buildings, points start flowing in like they do in Arathi Basin. The flag in the center of the map can be captured and taken to any of the buildings under your teams control for some extra points.
The narrow bridge on which the flag resides is an excellent location to lplay around with Seed of Corruption.