“Get In The Bag Nebby,” sometimes iterated as “Nebby, Get in the F**king Bag,” is a catchphrase used by the fans of Pokémon Sun & Moon in reference to a recurring Cosmog Pokemon-character named Nebby, who became a popular subject of Sun & Moon fan discussions for its tendency to venture out of the travel bag carried by its caretaker, Lillie.
The joke originates from Pokémon Sun and Moon, the first pair in the seventh-generation of the video game series released on November 18th, 2016. In the game, an assistant character named Lillie carries with her a Cosmog, a Psychic-type legendary Pokémon character whom she nicknamed Nebby, concealed in her travel bag to keep its existence under veil. However, throughout the course of the game, Nebby repeatedly manages to sneak out of the bag, which quickly becomes a recurring source of frustration for Lillie and other trainers as they try to keep Nebby’s existence a secret.
In the days following the release of Pokémon Sun and Moon, many players began sharing their amusement or frustration at Nebby’s frequent escapades on forums like GameFAQs, Reddit and 4chan, as encapsulated in the phrase “Get in the bag, Nebby,” as well as visual jokes mocking the poor design of the bag and its inability to keep the Pokemon contained.