Green Rooming

Introducing a new character who is then inexplicably ignored for a few episodes. Often the result of a clumsy Debut Queue setup.

Alternatively, a common use of Lampshade Hanging to explain why a cast member useful to the plot isn't around. This can be to exclude a character who would make a plot end too early or because the writers want to focus on specific characters.

Poorly used, this will introduce a character who is used for a single arc and then forgotten for long periods of time. The kind of writer prone to this is also liable to keep doing it.

Not to be confused with shows shot in a green room.

Anime & Manga

 * A skillful usage of this technique is in Love Hina, where Motoko (along with her "groupies") is introduced in the first minutes of the first episode, but she immediately leaves on a training excursion, thus freeing up screen time for introductions of the other characters before she gets her turn to take center stage in the third episode. Shinobu is also seen in the first episode, but not really introduced until the second.
 * In Kämpfer, Mikoto is seen in the first few episodes via postcards to her childhood friend Natsuru. She's seen again at the end of episode 5, but Mikoto doesn't see Natsuru till episode 6. She remains part of the cast after she returns home.

Live-Action TV

 * In Doctor Who, Robot Buddy K-9 is introduced in "The Invisible Enemy", then promptly breaks down for the duration of "The Image of the Fendahl", whose script was written before K-9 was added to the cast.
 * Also, Robot Buddy Kamelion is introduced in "The King's Demons" and then disappears for almost an entire season, reappearing only in order to be written out. This was because the complicated and expensive Kamelion prop actually did break down, and the only person who knew how it worked had died.
 * Script editor Eric Saward said in an interview in Doctor Who Magazine that Mike Powers' death wasn't the cause of Kameleon getting sidelined. The robot prop hadn't worked right from the beginning, and the character had been created based on the operators' exaggerated claims of its capabilities. Powers' death provided an easy explanation that didn't lay blame on anyone.
 * Happened quite a bit in Code Name: Eternity due to the episodes being aired out of order. The two main characters meet a sidekick early in the season, followed by a replacement sidekick in what should have been about halfway through the season; but instead, the sidekicks seem to appear and disappear at random.

Video Games

 * Touhou Project has this to a large degree thanks in part to Loads and Loads of Characters, as well as The Rashomon endings to most games, where characters like Ruukoto, whose mere presence would deny the canon status of all the other endings. Stage 5 characters are almost guaranteed to become Recurring Characters, but any EX-boss not named "Yakumo" will probably never be heard from again in canon, aside from a page referring to them in side works like Perfect Memento In Strict Sense.

Western Animation

 * G.I. Joe had a habit of doing this, with its ridiculously large number of characters and all.
 * Transformers suffered from the same thing, some characters only appeared for one episode!
 * My Little Pony Friendship Is Magic has several examples, considering it has Loads and Loads of Characters. Most prominently:
 * Princess Luna makes her first non-Nightmare Moon appearance at the end of the pilot two-parter, is reunited with her sister, Princess Celestia, has a party in Ponyville in her honor... and is never mentioned again until Season 2. But then, when she came back, she came back with a bang.
 * The zebra Zecora has an entire episode dedicated to introducing her, then she reappears for one quick scene the next episode... and then doesn't reappear until the same episode Princess Luna returns in. Season 2 as a whole has given her considerably more screen time, at least.