Magic: The Gathering - Duels of the Planeswalkers

This can be done both online, or through the co-op campaign.

For the co-op campaign, you can play online with someone else against another team of two players or play the co-op campaign locally with two controllers.

Addendum by thatkidfromohio:

You can set this up under player match online and if you both have an extra controller you can boost it.

So there you go, it IS available online according to one user, just have to jump through some hoops (extra controllers) to get it.

Must be done in a local game.
An easy way to get this is to choose Co-Op Custom Duel and set your life to 40 with hand size of 9 and the AI life to 20 with a hand size of 5.

I used the Claws Of Vengeance deck (Red, White & Green - all cards unlocked) which you get after beating opponent 14 in the original single player campaign (Tezzeret The Seeker with the Blue & Black Relics Of Doom deck). My 2nd pad was using the basic green deck (Teeth Of The Predator) without any unlocked cards.
My opponents were the Teeth Of The Predator deck (Garruck Wildspeaker) and the Hands Of Flame deck (Chandra Nalar).

Ignoring the massive advantage you get right from the start, I used the 2nd pad to throw creatures down and reinforce them with +X/+X cards. My Claws Of Vengeance deck never even got a creature onto the battlefield but did get a few cards that deal damage directly to a player or creature.

I'm no good at this game and don't understand all the rules and tricks that can be used but I still battered the AI on my first attempt.