Wow this one was a pain in the butt for me. For the first part you will use your wand to repel the Dementors as they fly at you, they get faster and faster each round so watch out, just keep an eye out for them, that's really the only tip I can give you. For the second part, make sure you use your mini-map in the bottom right hand corner of the screen. Make sure you lean during this part, don't move your entire body. I ended up scoring a 92 for Dementors slowed, a 100 for Dementors repelled, and a 50 in health remaining and got the five stars. This is the last minigame for year 3.