When you are facing a large enemy, you have to figure out how to activate your speed kill for that specific enemy. On one of the first bosses (the giant guy with the HUGE sword that you fight in the colisseum) you have to climb up until you are able to jump onto him. When you're on him, DON'T just start trying to attack. You have to wait until the time goes into slow motion (your speed kill activates) then you swing the remote and attack. You're going to do about four or five different attacks in a row, so be patient and make sure to wait for the slowed down time sequence. If this doesn't help just let me know. I beat the game like four days after i got it