I'm stuck at the giant snake (first boss) in Trine 2. Any ideas?
Climb the steps on the left and the snake will try to bite you.
After the second time, the cave should collapse.
There are a couple of ceiling supports there. You need to smash them all to cause a cave-in which kills the snake.
This can be done using Pontius's Storm Hammer. (Also Zoya's Exploding Arrows, but you won't have those on your first playthrough.)
Alternatively, you can stand on the platforms to lure the snake into smashing them. But watch out, its lunge will hurt you as well and it can be a bit tricky to dodge.