Way of the 9th grade ninja (Ancient Ninja)

Long ago an ancient caste of warriors swore to a cause that would evoke warriors to take on the mantle of a hero. That hero being known as the Ancient Ninja. The Ninja is a powerful being shrouded in secrecy as it is against their code to unveil who they are. Every few centuries, a new Ninja is selected to uphold the mantle of the ninja. Previous Ninja's have their experiences permanently etched into the document of all Ninja knowledge known as the Ninja-Nomicon. Every Ninja learns from the past, able to use techniques of their predecessors, or invent their own new ones. As the Ninja they are tasked with one job, protect who cannot protect themselves and uphold peace amongst everyone.

The Nomicon and Mask

At 3rd level, your mask once equipped forms the ninja's suit (design can be decided by player and dm) which provides the wearer a +2 to their armor class on top of their natural one. With the mask comes the ninja's arsenal allowing you access to the ninja's weapons and tools.

• you gain proficiency with the ninja's sword, chain sickle, shuriken, scarf (whip), and smoke bombs 
• smoke bombs: you have 5 charges of smoke bombs. by using one on a bonus action, you mask your presence, allowing you to avoid taking an attack of opportunity when escaping. after your five charges are used, you regain them after a long rest.
• Swords (long sword reskin), Chain sickle (like normal sickle but can be used at 10 feet instead of 5), shuriken (reskin daggers), Scarf (utility whip)

The nomicon is the second item the ninja gains upon becoming the ninja. During a long or short rest, the ninja can "schloop" into the namicon to learn from their predecessors. It'll become more important later, although at this level the dm can use it as a method of rping with the player. Such as teaching them how to hone their skills and giving them (albeit cryptic) tips on their efforts.

Ancient powers

During a long or short rest, the player can Journey into the ninja-nomicon to assign skills and tools to their move set in order to aid themselves in battle. Be it used from the magic within the mask, or the tools it creates, it takes ki points to activate their effects. Once assigned they cannot be changed until the ninja "schloops" into the nomicon once more.

• you have 2 slots for your skills, you gain additional slots at 8th, 10th, 12th, 14th, 16th, and 18th level
• your skills can vary greatly as each one will be unique depending on how you set it up
  skills available to the ninja include:
• Ninja boom balls: 1 ki point, creates a focused blast from a grenade like ball (radius 15x15 area, on a failed dex-save enemies take 2d8 fire damage and half as much on a success.)
• Ninja frost balls: 1 ki point, generates an aura of cold on combustion (15x15 area, water in the immediate area freezes over and fires are put out, enemies caught in the blast must make a con save. On a failed save, enemies take 2d6 cold damage and will be prone due to freezing in place. On a success they take half damage and are not frozen.)
• Ninja thunder balls: 1 ki point, spawns an arch of lighting down towards the highly conductive material it's made of (5x5 area, on a failed dex save enemies take 2d8 lightning damage and half as much on a success, on a nat 1 they are knocked prone from paralysis.)
• Ninja bee balls: 1 ki point, summons an angry hoard of bees to attack your enemies and possible allies (10x10 area, a bee swarm is summoned in that spot and are added to the Frey.)
• Air fist: 2 ki points, the air fist is one of the more powerful techniques in the ninja's move set, allowing the ninja to send a projectile fist at an enemy (by rolling a ranged hit check, the ninja can send a fist of pressurized air at an enemy dealing 2d8 force damage per ki point expended to an enemy, on a crit it can send an enemy 10ft in the direction they were hit.)
• hydro hand: 2 ki points, send a scalding blast of water at the enemy as a projectile (by rolling a ranged hit check, the ninja can send a fist of boiling water at an enemy, dealing 2d6 acid damage per ki point expended.)
• Earth attack: 2 ki points, by inciting an ancient poem you bend the forces of earth to your will (you can summon 2 soldiers of sand (your stats, 1 ninja sword, 10 hp) or create projectiles of sand/dirt/mud/earth dealing 2d8 bludgeoning damage per ki points expended.)
• Art of healing: 3 ki points, by using this skill you can heal the damage of allies and fix injuries that could be permanent (heals 2d6 hp per ki points expended and fixes injuries.)
• Art of stealth: 3 ki points, by using this skill you are near undetectable by your enemies (provides advantage on stealth checks and disadvantage on enemies' perception checks for a minute.)
• Art of escape: 3 ki points, no one's grasp, or a holding cell cannot hold you (advantage on strength checks against being grappled or escaping a cell.)
• Ninja Tengu Fire ball: 4 ki points, the ninja's most devastating attack, throws a massive blast of fire and heat at enemies (casts 4th level fire ball)
• Ninja Rage: 4 ki points, the ninja is enraged and unleashes a devastating array of attacks (apply haste and gain a second action + bonus action.)

Ninja's super senses

At 11th level, your passive perception and passive insight is increased by +4 while wearing the mask. This allows you to register potential threats way before they reach you and your party. On top of your heightened senses, your deflect missiles becomes stronger. 

• damage is now reduced by 1d12+your dex mod+monk level
• you are also able to now deflect magical projectiles
• normal range is 20 ft and long range is 120 ft

With these heightened senses and improved natural skills, it becomes harder to trick and defeat the ninja.

The Ultimate lesson

Upon hitting level 17, the ninja hones all their skills and partakes their final lesson. By giving their life to the cause of the ninja, their lives outside of the ninja are now one with the cause. You are able to access you powers and skills while the mask is unequipped. No longer being restricted by needing the mask you can make proper use of your powers and skills. This allows them to pass on the mask and the nomicon to the next upcoming ninja, using their skills to further their goals without the mask.