Onyxia Scale Cloak

While some capes provide more fire resistance, the Onyxia Scale Cloak is essential for most of the bosses in Blackwing Lair since this cloak prevents Shadow Flame from engulfing the target (the DoT after Shadow Flame hits).

Source
Onyxia Scale Cloak is crafted with Leatherworking (300); taught by Major Mattingly, after having turned the Head of Onyxia (original) over to him.