just cast spells...if u have fred &george with u use their lvl III(3) spells if not then
just cast random spells...hope this helped

I'm not sure what duel you are doing, but when you have a DA session, get to the
highest level in Stupefy. Then you can use it. Down the bottom, select who you want
to use to fight. The green bar means health, blue is Power. If you have little power
you can't use your spells.

This is for Nintendo DS

I am also stuck at this point - its when remus and sirius face the 3 deatheaters in the
ministry. I have tried and tried again to kill the 3 deatheaters and nothing seems to
work. I am seeing my 12 yr old newphew soon (game ace) an get him to do it for me. Once
he has I will let you know!

pick off the dementors 1 by 1 and use progeto (preferably lvl 3)every 2nd spell