Demonic Figurine (Warcraft III)

Summons a Doom Guard to fight for you. Lasts 180 seconds.

Source
Illidan, Kael'thas Sunstrider, Lady Vashj and Akama can find one in Lord of Outland, chapter 6 of the Frozen Throne alliance campaign, Curse of the Blood Elves.

One of the items purchasable on the Marketplace.

In the RPG
This intricately carved black onyx statuette depicts a baleful demon with claws outstretched and a single hoof raised as if to stomp upon the ground.