This is not going to be pretty...
That's what you get, Mario
If those were Koopas, then they would be those paper-thin ninja ones from the first Paper Mario.
These guys are once ordinary baby turtles who were mutated by some mutagen and raised and taught the way of the ninja by a human ninja master who was mutated into a humanoid rat.
That was just a little role-playing of Mario trying to get out of an oncoming butt-kicking with a technicality.