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.
Just like in BTD5, it costs $2340 on Easy, $2750 on Medium, $2970 on Hard, and $3300 on Impoppable.
Generally, Seeking Shuriken is better as it allows the Bloonjitsu to make use of its fairly large pierce and several projectiles.
This becomes more relevant when the Ninja is Alchemist buffed as its max pierce becomes a whopping 35 (across 5 projectiles).
With Seeking Shurikens, the Bloonjitsu can also have Caltrops for slightly more overall popping power via regular caltrop attacks onto nearby track.
Arguably, Distraction is more useful lategame because it falls off from being reliable DPS later on.
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 do not 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, though either are not bad options with Alchemist brews even with fast expiry.