Throughout the SeriesEdit
In Jake & Amy, it's mentioned he was going to be the ring bearer at Jake & Amy's wedding but he got the chickenpox. Jake had said he wasn't super jazzed about Mason. Amy agrees and adds that Mason should be cuter. Jake said Mason's face is too small for his head; that he's a "Dick Tracy" villain.
In Casecation, it's mentioned that his birthday party was ruined when Jake and Amy shot all the kids while playing laser tag. Jake adds that it was deservedly so because Mason was a jerk.