hold r1 to aim then jump over him and use helm breaker to land on his back whilst doing damage. then you can slash away until you fall off. repeat and he's a peice of cake
ps. sometimes if you do it right you can put him off balance and he'll rear back in pain. then is a good time to get a few hits in at his face!

ps. sometimes if you do it right you can put him off balance and he'll rear back in pain. then is a good time to get a few hits in at his face!