Now this one actually made my arm hurt after doing it a few times. First of all, you will be scored off of time remaining at the finish, how many potions you dodges, and how fast you helped Neville. The trick is to wave your arm sideways to hit the pixies, not vertically. When you need to help Neville, wave your arm horizontally back and forth as fast as possible. Ignore avoiding the potions and focus on getting as many pixies as possible. I got a 100 in helping Neville, a 100 in time remaining, and a 54 in dodging potions and got the 5 stars. This the first minigame in year 2.