I'm so excited about this pet that it's getting silly. Last time on "Tiny Phoenix Obsession," we discovered that it's acquired as a drop from Kael'Thas, in his incarnation as the final boss of patch 2.4's 5-man Magister's Terrace, and speculated that it's probably a pretty rare drop. WOWDB has it at a 1% drop rate, apparently in both normal and heroic mode, although it doesn't say how many kills that's based on.
Now we have in-game video! It's just as appealing as its picture, and I really like the fiery aura that surrounds it. And that calm, confident hovering...I must have it! Look out, Kael'Thas, the day 2.4 goes live I'm coming after you, and I'm taking your cute little fiery bird. Are you prepared?