You can't find a black Koopa Troopa (unless there's some bonus level I'm not aware of), you have to make one. All you need is Yoshi and a level with a Shell-Shocker (those spinning Koopa Troopas), but it's best with a cape at the place where the Super Koopas are coming after you and there is a Shell-Shocker in the beginning, I can't remember the number of the place. Anyway, at the beginning, have Yoshi eat the Shell-Shocker, then spit the NokNok shell out. It's usually a "normal" color, but every so often it will come out black. There's this place in that world with a hill and a block to stop the shell, and what you want to do is have Yoshi spit it out and then spin-jump off him and have the cape brush the black NokNok shell, and it will come down upsidedown and stay still. Now, there's a Koopa Troopa (green I think) in the area, and you want to get him out of his shell, and if you do it right, he'll head over to your black shell, get in it, and you have a black Koopa Troopa. It's just like a regular one, and there is no reason to do all this besides getting a cool-looking black Koopa Troopa. In case you hadn't figured it out by now, it's not easy. I only managed to do it once (by accident) and ended up with the shell, but I never tried to make a black Koopa Troopa (I just let go of the shell to kill the Para-Goombas, hoping it would do something cool that the other color shells don't, which it didn't), but I don't see any reason why you couldn't create a black Koopa Troopa with it, since you can do that with other shells. To my knowledge, there is no black-colored shelless Koopa Troopa, but don't hold me to it. I figured all you people on this board were hard-core "Mario" fans that would know stuff like this.