They all are capable of different attacks, usually elemental-based.
Ask the Breeder about the Pokemon you like! ^^
Sounansu, for example, is good for nothing but defending. xD; It is physically incapable of attacking first. It must wait until someone else attacks it. It can then use Counter or Mirror Coat, reflecting the Pokemon's attack right back at it, even stronger than when it first came its way if it pleases!
As a last resort, it can also use Destiny Bond. This attack is rather useless, but if you would rather tie than lose, Sounansu will cause the other Pokemon to faint the same time it does, bringing the battle to a draw.
Mine hasn't ever used Destiny Bond, but it has used Mirror Coat, Counter, and Struggle.