You have chosen to follow the ancient monk way of stealth and assassination. This group of monks, called Ninjas, can move across the night without being noticed, and use weapons no other monks use.

Ninja Proficiencies.

Starting when you choose this subclass at 3rd level, you gain proficiency with Katanas, Naginatas, and Nunchakus. These count as Monk weapons for you. You also gain proficiency in the acrobatics, stealth, and survival skills, if you do not have them already.

Ninja Speed Battles

Also starting at 3rd level, you may spend an extra 2 Ki points when you use your Flurry of Blows ability to use it with a Longsword, Warhammer, or Dagger.

Extra Sneaky and Extra Acrobatic

Starting at 6th level, you may spend 1 Ki point to add 1d6 to a stealth or acrobatics check you make.

Speed Attack

Also starting at 6th level, you may spend up to 3 Ki points to add to a Initiative roll you make

Dexterous Fighter

Starting at 11th level, you may treat all non-heavy, superheavy, massive, or two-handed weapons you have as if they have finesse.

Master Ninja

At 17th level you have become the master ninja. You may wield any two monk weapons you have at once, as long as they are not heavy, superheavy, massive, or two-handed. In addition, you gain expertise in stealth and acrobatics, and have advantage on all checks you make to disguise yourself from others.