Cardian

This deck was shown to me by Live2Die.  A lot of credit goes to him.  I tweaked the deck a little bit and figured out the best way to 'play' it. This strategy was very successful when I tested it on the last six battles(not losing a single one).

Here is what your deck should look like
Gold Mine(11) "Increases your gold production by +2 a second"
Crystal Mine(4) "Increases your crystal production by +2 a second"
Peasant(14) "25 gold to play, 10 gold to summon a single Peasant"
Parting Gift(2) "While in effect any unit killed deals 1 damage to its enemy's portal"

The strategy goes like this. You have two ways to win. One, spamming Peasants or two, damaging the enemy portal through the death of your Peasants while the Parting Gift card is in play. Strategy two works best on the last few battles while strategy one works best on the first few.

At the start of each battle you are going to want 3 or 4 Gold Mines. If you don't get a lucky draw your first time keep restarting until you get a starting hand with 3+ gold mines. Next you are going to want to keep drawing new cards until you get a Cryatal Mine. Play it as soon as possible(Note: you should only play one of your Crystal Mines, the rest were to increase your chances of drawing one sooner rather than later). Next, wait until you draw a Parting Gift card. Once you have one in your hand, play it(requires 25 Gold and 40 Crystals). Once this card is in play you can either summon five Peasants and send them out as fast as you can(in a rush type strategy), or summon five Peasants and send them out in groups of five or ten(to make sure that they die, which damages your enemy's portal.

The beauty of this strategy is that both strategies are working at the same time, even if you are rushing the enemy portal with Peasants some are bound to die resulting in loss of health for the enemy portal.

Using this strategy you should be able to power through battles with little to no effort. Once again, thanks to Live2Die!