Ninjitsu is one of the best PVM skills there is, especially as you already have 120 Ninjitsu.
At 120 Ninjitsu you have a 90% chance of diverting melee attacks, when you successfully divert the monster stands there doing nothing as if targeted peaced while you continue swinging.
On top of that cat/dog form at 120 Ninjitsu gives you 40 hit point regen. (4 hp per second.) If your character is human you get another 2 & you equip the maximum amount on items 18, then you can have 60 hp regen.
The combination of mirror images and cat/dog form make you pretty much invincible. However your template could use some tweaking.
Firstly I would consider switching Fencing for Macing as it has higher base damage on most weapons and you can still reach the swing cap fairly easily with a little ssi.
If your using Fencing as you just prefer it then I would drop tactics to 100. You can also drop Stealth & Chivalry some. How far depends on how much you use it and what for.
Chivalry spells 100% success is at minimum skill +50. If your using it JUST for sacred journey then you need 65, 65 also coveres heal/cure/remove curse/consecrate. You can still use divine fury & enemy of one at this level. If your fussed about the reliability of divine & enemy of one then 75 will give you 100% success at divine and 90 will give you 100% success at enemy of one. Most people go with 70 or 75, though I personally use 65 and still use enemy of one and divine.
Stealth can be at 80 unless your using a non med suit, the virtue suit being the exception as it is stealthable at 80 but not medable. It is also handy as it has roughly all 90's resists blessed & self repair so you can be corpse skin proof, but you lose out on other suit mods.
I also always recomend resist at 100 minimum in PVM as you can't cast anything when you get mana drained.
Here is what I suggest:
120 Ninjitsu
120 Macing
115 Tactics
100 Resist
100 Hiding
80 Stealth
75 Chivalry
If/When you can get a 120 scroll for Tactics I would drop 5 from Chivalry in to it.
Poisoning is not worth it on a Ninja as you can use Shuriken & Darts to inflict any level poison that you chose to apply anyway.
As for your suit it depends greatly on what you can afford but I would personally want 4/6 casting or as close to it as possible to make good use of mirror images, also makes changing forms quicker and you can also use Chivalry heal/cure/remove curse to much better effect. So if you were fighting something that poisons/casts a lot you might want to use Chivalry & images instead of the cat/dog forms, though if you went all out on hp regen items you would probably be able to live fine either way. You will also want a fair amount of lmc and mana regen, I suggest using the rune beetles carapace as the starting point for whatever suit you can build. Ideally an ornament of the magician too.
Don't neglect to use the other forms and learn how they work, Ninjitsu isn't the one trick pony that most people see it as. You can combine most of these with mirror images to stay safe while using them.
Serpent form: Everytime you hit something you inflict level 1 poison. (doesn't work with Archery)
Frog form: Everytime something hits you, you inflict level 2 poison. If you were say working a spawn and wanted to poison everything you could take off your weapon, this means you get hit everytime. If you run through huge groups they all poison themselfs then you can re-arm and change to cat/dog to heal if necessary.
Wolf/Bake: +20 hp, +20 HCI, mounted speed.
Ki-Rin: +20 stam regen, mounted speed.
Unicorn: Immune to low level poisons, mounted speed. Doesn't cure a poison if you go in to the form afterwards.
You can also use smoke bombs to hide while flagged/fighting, not entirely necessary as you can just use a mounted speed form to run around the nearest corner and hide. You don't need to be wearing a ninja belt to throw stars but you do need to have one hand free, I expect it's the same for darts too though I only ever used stars. Darts are for close range (under 2 tiles) & stars are for long range (everything over 2 tiles).
Oh and in case your not already using it I suggest making a macro for toggle always run, so you can turn easier when running in mount speed but easily turn it off for stealthing.
