We’ve already talked a bit about Greninja’s tongue here. Greninja uses its tongue like a snake, to smell/taste the environment around it. The bigger the tongue is, the better Greninja could smell with it, so it evolved to be so huge that it no longer fit inside Greninnja’s mouth. But, since Greninja is a frog, its skin is covered in a layer of slimy mucus, which keeps Greninja’s tongue moist and clean despite being exposed to the air all the time.
Instead, I want to focus on Greninja’s ability to use water as a ninja star, a fast and sharp projectile weapon.
Water itself isn’t incredibly intimidating. The worst water guns do are get you wet, and even when dropped from thousands of feet in the sky as with rain, water simply won’t get fast enough to do any damage. Even if shot with high velocity, water quickly loses speed in air simply due to the nature of it. Water is a fluid, so under most circumstances it simply splashes off of something. And since water is not very dense compared to other materials, even if it does penetrate, Newton’s laws say it won’t go very deep. Still, like Greninja’s dex entry says, under the right conditions water can be used to even cut steel.
So how does Greninja do it? Water does have one thing going for it: water is incompressible, so its density and volume will not change. There are exceptions of course, but it’s generally a good assumption to make. Water will not squish or absorb impact like a marshmallow or a spring; it will act more like a bullet.
The issue becomes keeping water from separating and splashing into droplets. Especially since its spinning, one would expect the water to fly apart quickly in the air (think of a pizza dough being tossed, and flattening out). Greninja could actually use ice projectiles, that simply melt just before/on impact. But, if it’s shurkins are water, and not ice, high pressures and temperatures will do the trick. Water jet cutters, like the one pictured above, use high pressures and temperatures to shoot out streams of water. The high pressure enables the water to essentially pushes itself forward, which lets it cut the steel rather than splash off of it.
So for Greninja to weaponize water, it must shoot/spin the water so fast that the water is forced to continue its rotation before it gets a chance to fly off into droplets. This would require huge temperatures and pressures, certainly adequate to slice into the target on impact.
Greninja shoots water at high temperatures and pressures, which keeps the water from splashing apart before it impacts the target.
