Blackwing Spellbinder

Blackwing Spellbinders appear as blood elf mages and are located in the Crimson Laboratories of Blackwing Lair after defeating Broodlord Lashlayer. They initially appear humanoid, but will reveal their true draconic forms when attacked by transforming into dragonspawn.

Note that spellbinders are completely immune to magic.

Abilities

 * Flamestrike
 * Greater Polymorph

Notable drops

 * Band of Dark Dominion
 * Doom's Edge
 * Essence Gatherer
 * Hourglass Sand

Speculation
Their classification as dragonkin implies that they are dragonspawn disguised as blood elves.