I can totally see Clemont's Chespin getting jealous of Serena's Pancham when it comes to showing off it's moves in performances and starts to show his moves in which Serena and Clemont notice and decide to let Chespin participate in one with her. This could be a perfect way for Chespin to bond with Serena and Pancham and will lead Clemont to be more invested in Serena's performances than ever before!
there are a lot of ways for Chespin to get involved in Serena’s Pokemon Performances. I think the best way to write it would to start showing that Serena’s routine is lacking or can’t rely on Braixen and Pancham all the time. Maybe that’s when they begin to realize that Chespin can fill that niche with Pancham.
The problem is, they’re also going to be introducing Eevee soon. So the struggle is figuring out how to get Pancham and Chespin on-stage without quickly marginalizing Eevee after it’s introduced.