This must be done on the hardest difficulty. Remember once again you can save at any point and quit and reload if needed.To kill the chopper you must hit the glowing nose section multiple times. As the chopper first comes down and then starts to rise again you can get usually 3 hits, sometimes 4 if your lucky. Now some yellow ninjas will come out of it, as soon as they do crouch and fire stars fast and you will kill them quickly but be careful because as the chopper starts to come down again it fires rockets which have to be jumped over. Now use your magic and the chopper should only have 2 hit points left, move to the far left hand corner and another couple of accurate hits as it comes down again should see it off.