Dawn's Mamoswine is the fourth Pokemon caught by Dawn. It debuted in Hungry for the Good Life.
Dawn caught Mamoswine when it was a Swinub. It is a target to Team Rocket who try to capture it and the gang's Pokemon to take to the boss.
Mamoswine didn't obey its trainer at first and often ignored her. But after Dawn showed how much she cared for it, it began to trust her.