Gulpin is Yui's fifth Pokemon she caught prior to Full Moon's Full Pokemon Journey, he was caught sometime around the episode Mami's Choice!. It is Yui's first Poison-type Pokemon she has. In "What's In a Nickname?", he was officially nicknamed Glomp by Yui, and even nicknamed the other Pokemon she has.
As of season 3, Gulpin evolved into Swalot after protecting Yui from a swarm of Beedrill.