Trine 4: The Nightmare Prince

Story-related and cannot be missed.

This trophy is for completing the fourth level in Act II, The Prince's Dream.

At the end of this chapter, in lieu of a boss fight, you'll have to solve a series of puzzles, all attempting to get the beam of light through one portal and out the other into an open cauldron, with each getting progressively harder and more complicated. This is Amadeus' boss, so he is the only one you'll be able to play as; you won't be able to switch to the other two until it's done. Once you complete them, exit the door on the right side and the trophy will pop. For the full solution, see the video below: