Shedinja is really just a gimmick pokemon. But in the hands of the right trainer, can actually be pretty deadly. He's great for switching into resistant attacks, since he's impervious to all damage from non super effective attacks. That means he can work great defensively despite his sweeping stats. But it only looks good on paper, because most trainers have something to counter him, and he's also not protected from status or weather, making him an easy kill. But if you can clear your opponent's team of any threats before sending him out, Shedinja is unstoppable. As for the soul stealing thing, the pokedex entries are just there to give some interesting information about the pokemon, but isn't necessarily true for how the pokemon functions in the game. (they say that Nidoking can snap a telephone pole as if it were a matchstick.)