As seen in the flashbacks in As Cold as Pryce, Pryce had his Piloswine even when he was a young Trainer, and treated it like family. One day, when they were up against a Magmar, Pryce protected his Piloswine from Magmar's Fire Blast with his own body, and as a result they were both burned badly. Piloswine left to find herbs that would help heal Pryce's burns, but got frozen on the way back, leaving Pryce to think it abandoned him.
Years later, Ash and Pryce found Piloswine frozen in a cave and set it free. Pryce and Piloswine were reunited. Later Pryce used it in the Gym battle battle against Ash in Nice Pryce, Baby!
It defeated Cyndaquil easily and put up a fierce battle against Pikachu before Pryce forfeited as Piloswine had become tired.