He's a power house because most pet battles on Pandaria are soloable by him, and you can virtually duobattle any Pandaria battle (except Earth Spirit, which can be hard) with him + Flayer Youngling, making that a free xp boost to level 25 for 2 pets level 5 (which is enough to survive most attacks).
1400 HP / 341 Atk / 244 Spe
Emerald Bite / Emerald Presence / Emerald Dream
He's very consistent both offensive or defensive and, since pet battles atm are very predictable, you can virtually negate the damage done to him. Take the Fire Spirit Pet Battle for example, here's how the Fire Spirit will behave:
Turn 1: If pet is level 25 -> Use Conflagrate / If not, use Immolate.
Turn 2: Use Cauterize
Turn 3: Use Immolate
Turn 4: Do nothing
Turn 5: Use Conflagrate, dealing double damage.
Turn 6: Use Immolate
That's basically what he'll do, knowing that, you can do the following:
Turn 1: Use Emerald Presence
Turn 2: Use Emerald Bite
Turn 3: Use Emerald Dream (Turn 1) Regen 160
Turn 4: Use Emerald Dream (Turn 2) Regen 380
Turn 5: Use Emerald Dream (Turn 3) Regen 700
Turn 6: Use Emerald Presence
That'll make you be full and since you'll use Emerald Presence to negate damage from Immolate, you can dish out Magic Bites and kill him before he can even cast another Conflagrate. A similar script is appliable to every single fight in Pandaria. And since he's a dragon, when you down your opponent to 25% life you'll get the racial bonus for 2 turns, killing the first opponent and doing massive damage (Usually 500+) to the next pet.
He's pretty much immortal unless you mess up or RNG decides to be a dick.