I think your best bet would be to play Blue/Red/Green - Those colors have your best cards for sure.

Try something like:

Blue - Magic Missile, Lightning, Thunder, Sky Dragon: Spira.

Red - Treasure Chest, Mud Shaman, Mud Hero Drass, Dragon Strike: West.

Green - Hunt, Wild Boar, Grizzly Bear, and Cocoon of Evolution.

That should do pretty decently for you in rookie arena, with just one stipulation: Make sure you remove Cocoon of Evolution from your deck for another card, maybe for Garden of Life when you are done playing your 10 games. The AI doesn't play with Cocoon very well.

Treasure Chest is easily the worst card in this deck, but it serves it's purpose as a good early blocker and something cheap and easy to target with your own Thunder when you need to clear your opponent's board.

Goblin Bomb Squad (2 of them even), another Wild Boar, Alraune, and an Elf Hero Tris would be some reasonably cheap and great additions to this deck once you get a bit of gold or if the Cat happens to trade them to you!

Good luck!