When you start fighting he will say HOCUS POCUS and a shield will appear around him.
Don't try and headbutt it cause it doesnt work instead use your fire breath on it he will move to another place.
So follow him quickly before he can shoot you just continue doing this until his shield goes away then just flame him.
Now he'll say HOCUS POCUS again and another shield will appear around him now use your ice breath and do what you did on his other shield then when his shield goes away just attack him once and you've clocked the game.
P.S When you've killed his first shield you'll keep starting from when he's got the fire shield if you die so good luck.