Magmawyrm

Magmawyrms are a type of skeleton dragon raised from the corpses of black wyrms by the Scourge to serve as powerful minions, as seen in The Best of Intentions and Neltharion's Flame (quest). They appear similar to the emberwyrms, former red wyrms.
Nightbane in Karazhan may be a type of magmawyrm, although he was raised from the blue dragon Arcanagos.