Select the second chapter, and be sure that you are playing as the wizard. If you are not playing as the wizard at the start of the level, just switch to this character, and quit to the menu. The next time you select the chapter, you will start as the last character you used.
Play through the whole level as the wizard, use monster levitation (and boxes) to get rid of the goblins, and be sure not to switch to other characters. When you die (if you die at all), just enter the menu and restart the last checkpoint. The trophy will pop shortly after you defeat the boss and trigger the cutscene.