I'm having real trouble with figuring out how to beat the green deck in the archenemy campaign. It seems that no matter what decks I use for me and the computer, Garruk has over built and there is no way to keep up. So what decks should I use to keep this green power house under control?
I beat this using Chandra's Unquenchable Fire for all three rounds. Cast your damage spells directly on the opponent when possible. Also, your creatures should act as shields, so try not to use them too offensively.
Just keep using instants and sorceries to win each round. Throw in whatever cards you can to make this happen.
The trick is just having enough creatures between you and your pal to survive. Don't try to overpower Garruk's creatures, he can pop out way too many--that is what green is for, after all. Just go straight for him.
Also, if you bump the difficulty up, it might make the enemies a bit harder, but your ally will play better as well.
My friends and I had better luck with Nissa's Guardians of the Woods deck than with Unquenchable Fire.
Specifically, there is a card whose toughness and power are both equal to the number of elves on the battlefield - so when all three players are playing a lot of elves (which you will be), if any one of them manages to get that card, it's pretty over-powered.