The art of bloonjitsu allows Ninjas to throw 5 shurikens at once!
Bloonjitsu is the 4th upgrade on Path 1 for the Ninja Monkey in BTD6, allowing the Bloonjitsu Master to throw 5 shurikens at once. However, unlike BTD5, it is not possible to crosspath a Bloonjitsu with both Distraction and Seeking Shuriken.
Since DPS and shuriken accuracy via Seeking Shuriken are generally more important than a spray of shurikens with a chance of distracting bloons via Distraction, it is best to go along Path 3 instead of Path 2.
Bloonjitsu Ninjas are among the best candidates for Berserker Brew and Stronger Stimulant, even after the Version 6.0 Alchemist nerf. This is because they don't shoot so fast as to expire potions so early but at the same time shoots many projectiles at once with good overall pierce and damage. As a result, it is recommended that Bloonjitsus are not upgraded to the Grandmaster Ninja, and are not in range of any Shinobi Tactics ninjas, as these will cause the ninja to use up the buff quicker.