A fire giant.
We used two cards from a deck of illusion to destract it, while our party mostly attacked from range, hiding in thick forest overgrowth. We had an iron golem card, and a medusa card (of all things). It worked sufficiently enough, although it still put the hurt on a couple of us, myself included. It was essentially a random encounter. Come to think of it, the GM only took 1 attack per round (fire giants should get 3). It should have, by rights, killed at least half the party. *sigh*
Come to think of it, we didn't even loot the thing! Though the hill giant we encountered prior to this one didn't have anything of interest on it, so I doubt the fire giant had anything either.
The kicker is, we're only 5th level. 6th after that.