Scholomance Dark Summoner

Attacks and abilities
Spells they cast:

Summon Skeletal Lackey

(rarely) Curse of Blood

When they are MCed:

Curse of Blood, increases physical damage dealt to you for 10 min.

Drain Life, drains 100-101 health per sec for 12 sec.

Strategy
The Scholomance Dark Summoners are part of groups of either two or three mobs. These groups consist of the Summoners themselves and one or two Scholomance Necrolytes. The Necrolytes generally attack with Shadow Bolt.

The Summoners need to be seen as the priority targets of their mob group and removed as quickly as possible, since if they remain alive and attacking, they can gradually summon a large number of Skeletal Lackeys which will overwhelm the player group.

The Summoners' health is not overly high and so the player group should be able to tank the Necrolytes' fire for the short period of time needed to kill the Summoner.

If you have priests...

Mind Control the Summoner and make them fight the other two. Then cut in and attack them. Also, interrupt their summon spells — other than this, there's nothing special.

If you use a mage...

Simply sheep the Summoner and fight the other two. When fighting the Summoner, use Counterspell, Kick, Shield Bash, or Silence to interrupt the Summon Risen Lackey spell.

If you have a hunter...

If the Hunter is level 70, they can use Misdirection in conjunction with Multi-Shot in order to keep the attention of the Summoner and several of the Risen Lackeys focused on the main tank. A hunter at lower levels can also make use of Explosive Trap to rapidly remove a large number of Risen Lackeys at once.

Re. Patch 2.0.1
It should be noted that since the patch, the Summoners' in-combat behavior has been noticeably different than before. They now frequently run about ten yards away during the middle of the fight, which can cause a domino effect of additional aggro. Luckily, if your group uses the right strategy, this can be avoided. Simply incapacitate the Summoner using sap or sheep, take out the other mobs in the group, then put full DPS on the Summoner at the end. They can't run if they're dead.

Quotes
Scholomance Dark Summoner says: Hmmm, this one looks like something that would be better off as a windchime. Take note class... This is NOT what you want to summon in the heat of battle.

Scholomance Dark Summoner says: Note the weak binding structure of this one. Be sure to finish your incantations or this is what you will end up with.

Scholomance Dark Summoner says: Wow, this one is just plain useless. Let me try again.