Angered Nether-wraith was spawned by creating Spellcloth in Netherstorm.
It would drop 1-3 motes of mana and of fire when killed. Despite the desirability of its loot, most tailors would take efforts to avoid engaging it in combat - it had a tendency to wipe the floor with even then-max level 70 players. For a while, the crafting spell would summon two of these nasty arcane elementals before Blizzard fixed the bug. My preferred method was crafting the spellcloth as close to Area 52 as possible so the town guards would help me kill them.
At some point, perhaps late Cataclysm or the start of Mists of Pandaria, Blizzard removed Angered Nether-wraith from game. Lower-level characters may craft their spellcloth in safety.