You can play constructed (versus) and co-op modes (Oversky and Dragon's Lair) together against the enemy. You can't play Pandora mode against each other, of course not counting that time when you get matched together. I think that's it.

Previous reply is correct. Vs pandora would be really though. 

I'm looking to get into Faeria mainly to play with a friend of mine. I looked around for a bit, but couldn't determine what game modes would be available for me to play against him. For example, could we draft Pandora decks and play against each other? Would we be limited to constructed?

Friends and Game Modes