Perdition's Blade

Perdition's Blade is a one-handed dagger with a fire damage proc.

Source
The blade drops of Ragnaros in the Molten Core, Blackrock Mountain.

Notes and trivia

 * The blade's estimated drop rate is 15%.
 * It has a gold glow that trails the dagger when walking.
 * Perdition's Blade appears as a rare weapon for the Rogue class in Hearthstone. The flavor text reads: "Perdition's Blade is Ragnaros's back-up weapon while Sulfuras is in the shop."