get to the walls of the arena and climb those up to get to the monster,then kill it with several speed kills.

Hope that helped you.

You must be payient for the glowing. If you don't it will be your down fall. And as soon
as he is blinded, you must watch your step because the giant is most likely to charge at
you even though it canot see. You must attack its legs and as soon as it hits the ground,
jump on his back for the final blow.