Check the above link for the video.
Basically run either way and climb up a wooden ramp, use dagger plates if present to wallrun across, wall run/jump to a beam/wall, jump/wallrun to a platform, use daggerplate to run across a higher platform, walk to the beam triggering speedkill, perform speedkill pressing speedkill button through and using attack button when dagger flashes. 3 strikes per side will give you each eye. After blinding him roll behind all times and cut his legs from behind till he falls triggering a cutscene. The trick is [when his health is almost over ] to attack one leg till he raises it and stands on the other leg and immediately attack the standing other leg so he can bend on his knees [else he will never die at this point]. Here you don't have to press speedkill button. The game will initiate the daggerflash for you. You just need to be alert to attack when it flashes without hesitating a second or missing [thrice again]. You are done.
youtube has most of the videos on all bosses of PoP games so you should check there first if stuck.