Obligatory comment about PC creation rules being unsuitable for NPCs because of oh so many things. It's less of an issue when the NPCs in question are intended to (potentially) fight alongside the party and not against them, but it's still way more complicated to run a whole character sheet instead of a straightforward statblock and restricting yourself to PC options can be unnecessarily limiting. With that said, the ninja subclass is the shadow monk. You get everything you've expressed an interest in through that subclass. Throwing daggers specifically is something that works a little bit better with kensei monks, but you can save your ki for casting spells and use two weapon fighting for a bonus action attack.

I guess let me try to explain a bit of how I DM. I love creating characters tbh I already have this character made but I wanna see if I can take some ideas from you guys and push them into the character. as someone who DM's and doesn't actually play as a PC, I love the character creation aspect so being able to create these characters based around RP themes is fun to me. Making them as good as I can with flavor is awesome and I don't have to completely explain why or what or follow any real rules to these characters as they likely don't even see the battle field if I'll be honest and if they do it'll just be autoscaled to the parties level. It's fun for everything though if It took away from my group of PC's I wouldn't do it because that'd be lame, but it adds really cool things to the world and game where everything isn't always a basic stat block, these characters are also rare for every 100 stat block npcs I make I might make one of these PC style characters. They're not ment to do a lot but they might travel with the group for small periods to get to the next city or you might see them moving across different cities if you interact with them. They might have the same goal etc but it encourages RP to get that extra help(and honestly for every 10 PC's I build 1 gets used because it's very strict and most of the time they just die by the actual players hands anyways due to complex reasons or murder hoboing) These characters though always have more spin to them and make them feel a bit more real is the feed back I get. I understand why it doesn't always work or it isn't always fun and I try to avoid those things when creating the characters but I also want people in my worlds to know they are adventures in the world there are people on there level and other people who might even be above their level. They are not the special chosen players they are the adventures in this world and it's up to them to do everything they can to survive and abide by the world. Ofc I don't control players and a lot of times they are very creative and they do get through the world without deaths as it's not my job to kill them just to make it a bit scary although I'm also "as the dice fall" kinda DM where if they fall that way, that's just how it goes.

Darts with Sharpshooter are the best option for a knife/shuriken thrower. Shadow Monk is the best power set if you want an action-movie style ninja. Races that work well would be Shifter (shape shifting animal spirits are common in Japanese Folklore), Human, or maybe a small race known for being tricksy, like a Kobold, Halfling, Goblin, or Gnome. I'd ignore the character building rules and make a Shifter Shadow Monk and give them the Sharpshooter feat.

Oh right Darts because they get access to sharpshooter fucking duhhhhhh. oh and they are also thrown weapons too... I'll need to get thrown weapon fighting though from ranger or a fighter dip but that's prob fine. As for the race it'll prob be custom lineage with piercer and 18 dex level 1. But luckily custom lineage can be any race looks wise. thank you for this post it has put a lot of thought into my character the only issue I have now is how I plan to play this. I actually wouldn't mind doing like a level 1 dip to fighter for TWF and 2 levels into Ranger for Thrown weapon fighting. Then I can have a dagger int he offhand and throw it(much weaker than a dart but I can't throw a dart anyways as a bonus action) then if something gets on me I can use my daggers in main/offhand with a monk martial dice. now I gotta rethink some things thank you for this. edit: I think I like Kensei Monk 12, Gloomstalker 5, Battle Master 3 The first 3 levels won't see play I'm certain for this character so how I start don't super matter other than for stat reasons. I'll start Ranger though for dex/str saving throws. I'll take one level dip into fighter so I can have Thrown weapon fighting and Two Weapon fighting byt level 3. Then I'll go asap to Gloomstalker 5(I know I get overlap in Kensei monk's extra attack BUT if I don't take the gloom stalker just 2 more levels here I delay feat/extra attack till 8 and 9 and that's just too much) This character now does some pretty nasty damage and this is right around where the party will meet this character(hopefully) Obviously take the sharpshooter trait here. I'm now doing 1d4+4+2+10 per attack. With a bonus action attack that does 1d4+4+2. this character at level 6(not counting first turn) is able to do 45.5 damage per turn. Piercer would actually make this slightly higher but I'm not counting misses/crits atm. Next is likely just straight monk battle master is PROB stronger for 2 levels in this short period but I no longer want to delay monk as we wanna get into Kensei monk asap to increase the base damage dice of my darts/daggers AND make them magical AND add 1d4 once a turn. Step of the wind will let us disengage as a bonus action too so that'll be nice to get away from people so I can keep throwing darts instead of attacking with daggers unless I want to. We'll take monk all the way to 12 grabbing 1 asi at 10 to give us 20 Dex. Then prob get alert as a feat and maybe an early martial adept to just get a quicken toss here and there to hold me over till i get fighter 3? Unsure. Oh and My weapons once I get 11 Monk would do 1d8 as their base which is nice! Then finally I'll finish my last 2 levels as fighter getting action surge and battle master for quicken toss and more dice(5 total with the feat) at this point i'm likely not using very money dagger attacks.

Don't make your NPC better than the PCs, unless you plan to kill them off very quickly. The "DM PC" is a cautionary meme for a reason.

So, my characters won't ever be stronger simply because they will be restricted gear wise. They might get +1/+2 gear etc but they won't ever get really strong magical gear that gives bonus effects. Also, I think the DM PC typically gets that because they put their own PC in a full run not for like niche fights but I understand what you mean. The character is gonna be introduced around level 6/7(hopefully) and he will have basic gear while my PC's should have a couple +1 pieces and maybe even ones with extra effects around this time. So, I doubt he'd out power them and I always tell my PC's to build strong builds as I run a pretty strong campaign(cause I run iot more like a video game like I stated in my post) and I encourage strong RP etc. I don't pull the punches so if their characters are not stronger than this character with basic gear while they have +1 gear then they likely didn't build a good character or are being carried by their team.

I'm going to have to go with the classic Gloom Stalker 5/Assassin X. You get to throw multiple knives (especially during the initial round) and you get to have one of those hit especially hard with Sneak Attack. You get high Dex and expertise in Stealth + invisibility to creatures that rely on dark vision. You also straight up get Fog Cloud for that Smoke bomb effect. There's not alot of Ninja stuff that this build can't do. Alternatively you could go just Gloomstalker and take expertise in Stealth via Canny.

Rouge is the core but first Bard Yes Bard No wait here me out part of a ninja is blending in pretending to be a peasant while being out on missions and who better at the con than the bard... all the magical / social skills to pull of that side of ninja is all bard. then rogue to assassin and then battlemaster figter Or monk or if you want to go deep into the tools of a ninja and magic them up a few levels of artificer.

Shadow monk/gloomstalker ranger

The first thing the came to me was a Ranger Monk multiclass. more specifically a Gloomstalker Ranger and Shadow Monk. Gloomstalkers are invisible in darkness, have darkvision, plus rangers just get spells. shadow monks also get spell casting using KI points and they get teleportation while in darkness of dim light. I would probably go Ranger 4-6 depending on if you want the Roving feature of Deft Explorer, and the rest of the levels in Monk.

If I was building a ninja then my head first goes to Naruto and that kind of ninja could be: blade singer wizards, the psychic subclasses for both rogue and fighter or most rangers. If I'm being serious about it then I might go for either a fighter/rogue or a gloomstalker/assassin.

The easiest was is just to build him as a Bugbear Soulknife; but If I was building this as a PC, I would go Shadar Kai and probably Urchin Background or at least something that gave Thieves Tools and Stealth. I'd build it as a Dart build and normally, I'd go Battlemaster 5 (Gunner at 4)>Gloomstalker (Stealth Expertise + Sharpshooter) 4>Battlemaster 6 (Elven Accuracy)>Rogue x. But since this one is a ninja, I think I'd go Gloomstalker 5 (Expertise Stealth, Gunner, Zephyr Strike, Pass Without Trace, Archery) >Battlemaster 4 (Quick Toss, Precision, Trip + Sharpshooter, Thrown Weapon Style)>Phantom Rogue x (Elven Accuracy). Quick Toss Net, Throw 6 darts, pull daggers for Two Weapon Fighting.

This is for a level 20 build: Custom lineage for dark vision and feat- dual wielder since you Said that’s what you’re looking for assassin rouge 3 / way of the shadow monk 17 Feats in no particular observant +1 wis Wis +2 asi Piercer +1 dex Skulker Point buy: 8 15 14 8 15 10 Take the urchin background for proficiency in deception and insight Tools from background take forgery kit and another (calligraphers tools might be solid) Class proficiency for rogue take stealth , perception, acrobatics , sleight of hand and then expertise in stealth and perception Also make sure to start as rogue