Ok lets try and get it captured again.
Start by using Dig (unless theres some freaky rule about the arena's being only about 2ft deep, in which case use Sand Tomb again) and then send a Rock tomb up through the floor.
Then come back up and if its captured, hit it with Dragonbreath. If not, use Earthquake.

Dig/Sand Tomb - Rock Tomb - Dragonbreath/Earthquake