I don't know, I remember there being a Lich and a Druid at the end.

Yeah, something plant-like gave something useful.
I remember it being in a location where it's snowing.

I don't remember if I killed it. But my friend definitely killed it in front of me. He had a Gladiator, a Ranger, some kind of Mage (not a Lich, but a combat mage), and I think an Assassin or something. It was a long time ago, so I don't even remember all the classes. He was constantly hitting the dragon with some kind of magic, but since he had played the game for half a year before me, I had no idea what it was.