After receiving Kubfu and adding him to your team, he's been rather shy. Master Mustard said it'd take a bit before Kubfu would be fully ready for your battle commands. You had to befriend Kubfu first.

As you walked through the Forest of Focus, you figured you might as well look for a patch of grass to rest at. Kubfu was walking next to you. How were you supposed to befriend him? You had heard from his previous trainers that it was nearly impossible to befriend him..