This is done after you defeat Voldermort for the 1st time. Very simple Boss Level, just simply run around until he Throws a Green Head at you in which youwill reflect back at him with the B button. Jump the platform to touch him. Do this 3 times, and you win the level and the Achievement!
Year One Completed
***Thanks to MC Hammer - If played with 2 players, ONLY the main profile will obtain the Achievement, NOT both Players. Thanks for that******