In Poké Wars: The Coalescence, Dawn and Ash steal guns from the Safari Warden after they kill him with his own gun in self-defense. Later on the bridge, Dawn completely trashes a swarm of hostile Cloyster with a combination of dual wielded handguns and a pump shotgun. One problem, Dawn is a 10 year old Pokémon coordinator who has never used, let alone seen a firearm in her entire life. And yet, she manages to achieve "one shot, one kill". Also note that the weak point is only exposed for a few seconds and they are leaping into the air...and she nails every one of them. How the hell does a 10 year old Pokémon coordinator handle totally new and strange (to her) weapons with the poise, grace and unerring accuracy of a champion shooter?
It's explained in the last chapter of the Legendary arc. Lugia and his alliance release the dampeners in humans without making it painful. That's how Dawn gained her sudden shooting prowess and Ash and Samurai became more talented physically. It really makes sense.
In The Incipience, Regigigas and his golems started off giving Ho-oh and Mewtwo a run for their money, including Registeel being explicitly said to be unbendable by Mewtwo's psychic abilities. So how in the latter's comeback does he manage to "crumple him up like a wad of aluminum foil"?
Mewtwo just applied more force and yanked Registeel's arms off. And then beat him with his own arms.