there's some tips in that part? I watched many videos, but i can't understand how to do that ;(

If someone knows that tips, plz answer me

Well, I was with this problem just today and I could beat him after a while.

In my case I started with a flash and 21 slashes (just stopping to push the button) and after that another flash and 4 slashes or so... Then he got hit by the container. I believe 21 slashes is enough to do the trick but I need to test it yet. There are places where you hit him that deals more damage, just listen carefully for the sound the knife makes that you will spot it. Try using srt to see his life... he has to have around 10k to insta die.

hope this helps.

yeah, you can hit his shoulder and his body/head at the same time if you get the right angle/position.