It wouldn't need to use substitute, because at that speed as F=MA, it would be invincible imagine because 12kg (26.5lbs)*300000000m/s. Thats 3600000000N or 3.6 GN. Assuming newtons laws still apply in Pokeworld. But wait mass dilates as Ninjask approaches C aswell meaning that the Nijnask would be approaching an infinite speed.
But by now, time dilation and mass contraction seems boring. And do you know why?
Because we can't reach speeds near c (the speed of light)!
So I'm gonna delve into the vast Pokeworld
Yeah, I wish we could that far. But we can't (dang) if only it was in our syllabus!!!
Noooo! But I'll look at it once i'm out of school in my spare time after Uni.