Dark titan

Dark titans are titans that have been corrupted by evil.

Background
More Magic & Mayhem suggests that there are multiple dark titans, including Sargeras, trying to influence the world of Azeroth. These other titans may be ones that Sargeras corrupted and brought over to his will or perhaps they are just other rogue titans who have similar plans as Sargeras.

Appearance
Dark titans have bronze skin, However, since they've been corrupted, usually demonically, they have fiery bodies. Dark titans also have horns.

Trivia

 * Sargeras is currently the biggest threat to Azeroth.