Mushin F8.3 as Assassin nearly impossible?

[Asasel]

Hey,

 

I cant seem to beat Mushin F8.3 as Assassin, have fully max gear, 60% crit and he just keeps hitting me out of stealth and does this stupid ice attack. Hes way too op in my opinion. I once got him to 20% than time ran out, 4min is ridicolous, its not that we have lvl 50 patch yet. I like challenges, but not this unfair bullshit. If someone actually managed to beat him as Assassin, I would appreciate some tips...