Warlock's Succubus Pets
At level 20, you will get the rogue pet, the Succubus. Besides having a 'distinct' look, the Succubus is capable of dealing out damage. While it is contended by users, the Succubus is intended to deal out more damage faster than the Imp, but be less able to absorb damage than the Voidwalker. Basically the succubus is a middle ground pet. It is important to remember that she will also need to be summoned with a Soul Shard, so you need one ready to call her.
The Succubus starts with an ability called Lash of Pain. This is basically an instant-cast direct damage ability that deals about 30 damage (rank 1) to the target. Later the Succubus will gain Seduction which is a charming ability. This is useful against humanoid encounters, and can help you deal with multiple monsters at once.
The tactics around the Succubus are similar to the Imp: deal damage fast and share the pain between you. Approach the combat in the same way as the Voidwalker: open with a curse, DoT, follow up with DD, but in this case, do not hold back on the damage being dealt, even if it puts the monster on you. The damage absorption of the Succubus will only help slightly, so you'd rather just dish out the pain.
The Succubus is the best pet with which to practice a soloing technique called "drain tanking." Attack with the pet and apply DoTs of your choice. Eventually the aggro generated by your spells will pull the mob onto you, at which point begin spamming Drain Life to offset the damage you're taking from the mob, as well as Life Tapping to replenish your mana. Meanwhile, your Succubus should be ideally positioned to apply Lash of Pain to the mob's back. Drain tanking is only feasible as a play style if you take some key talents in the Affliction tree, but if done well you can take down mobs surprisingly fast and come out with only a small net loss of health/mana.
Succubi also seem to be very useful in a group where a tank is already present. Having the ability to dish out more damage, and even the occasional charm is definitely worth using. She also tends to create some oohs and ahhs because of her scantily clad appearance. The distinctive look of the Succubus will also make it clear what to target, and her reduced size compared to the Voidwalker makes fighting at close quarters easier.
Despite her lack of taunting, the Succubus can generate some hate on herself with her damage output (mainly when you have talents that increase her DPS: Unholy Power, Improved Succubus, Improved Lash of Pain). To keep your somewhat fragile pretty alive, Soothing Kiss will reduce the aggro toward her (similar to the rogue's Feint ability) and keep her dealing out damage without risk of dying. Always have Soothing Kiss on autocast when in a group, and never when playing solo.
An alternative strategy for using the Succubus is this:
1. Stay as far away from the mob as possible 2. Use Curse of Shadow on the mob (will also increase the Succubus' damage) 3. Let the Succubus attack at the same time 4. Wait a few seconds, so that it builds some aggro and does some damage 5. Cast 1 or 2 Shadow Bolts 6. Finish off with wand or Shadowburn, if needed
If timed perfectly, the mob will start running towards you in the end but spend some time running. If you share the damage with the Succubus, you minimize recovery time as you both regain lost hp at the same time. This strategy takes into account that the Succubus can't take much damage, and so using DoTs is too slow. Using the talents Improved Succubus and Improved Lash of Pain really makes this strategy shine.