Hmm sorry to say that ninja was not designed for mvp at all--but if you want to try it anyway, you have basically 2 options (if there are god items and stuff that are customized and out of the ordinary, you may have more options; but 2 is going by standard gears)
You can:
A)Attempt to get the most insanely highest HP possible, meaning Goibne's set or Tao Gunka, amongst others which I'm sure you can figure out on your own. Upon reaching the highest possible HP, you can try to Final Strike the MvP until it dies (basically you die and come back die and come back, unless you have a ygg berry/ygg seeds--but thats a waste unless you can get them cheap)
B)Buff your M.Attk like mad and go for the full ninja magic tree and instant cast. Spam Level 10 Ice spear like mad until it dies, using Hidden water when you get the chance and casting in it. If the MvP and/or its summons are slow, you can use the Fire Formation and continuously lure the MvP and/or Mob in circles while using the AoE Raging Fire Dragon skill.
These will both be tedious and time consuming, but if you really love ninja enough to go through with it, this is how you want to go about doing so. If you want to MvP/Hunt I recommend using Snipers or Champs--Snipers are better than champs, but are boring as hell so I usually go champ lol. Remember that a ninja that doesn't use Cicada Shedding Skin or its Stone-consuming variant is not a ninja at all.
If any questions just send a PM
