Clip show

A clip show is an episode of a particular series that is mostly made up of short segments from previous episodes, often to highlight what has happened during the series.

Prime time clip shows

In 1997 through 1999, 3 clip-shows were planned for Pokémon. Only two of those have aired, with the third one being cancelled due to the Porygon incident. Those clip-shows were hour-and-a-half to two-hour-long installments, aired after the regular Pokémon episode of the week in Japan and including many live-action segments. Much like Pocket Monsters Encore, the Weekly Pokémon Broadcasting Station, Pokémon Sunday and Pokémon Smash, they haven't been aired outside of Japan.

Regular broadcasting clip-shows

Those clip shows have been released typically as the second episode of a one-hour special in Japan (though AG120 stood alone). They have been used to recap what has happened up to a certain point in the anime's current series.

The New Year's Eve Special was planned to be aired between Holiday Hi-Jynx and Snow Way Out! but due to the Porygon incident, it was cancelled altogether. To date the other three clip-shows have aired solely in Japan:

Code	Screenshot	Title	Broadcast	Summary	Aired because
		おおみそうかだよ！　ポケットモンスターアンコール It's New Year's Eve! Pocket Monsters Encore	Unaired	New Year special, planned to air on December 31, 1997, but eventually cancelled following the 1997 Porygon incident.	Content unknown
AG120		サトシとハルカ！ホウエンでの熱きバトル！！ Satoshi and Haruka! Heated Battles of Houen!!	March 24, 2005	As Ash and his friends approach Slateport City, site of the Hoenn Grand Festival, Ash remembers his Gym battles in the Hoenn region, while May remembers her Contest competitions.	Both Ash and May are about to compete in their regional goal, the Pokémon League and Grand Festival, respectively.
DP048		サトシとヒカリ！新たなる冒険に向かって！！ Satoshi and Hikari! Facing a New Adventure!!	September 27, 2007	On their way to Hearthome City, Ash, Dawn, and Brock recall their adventures together so far.	Summarizes the first year of the Diamond & Pearl series.
DP120		ふしぎないきものポケットモンスター！ The Mysterious Creatures, Pocket Monsters!	March 26, 2009	The gang travels toward Snowpoint City, and along the way, remember what has happened so far in their adventure. Future events are also hinted towards...	Summarizes the Diamond & Pearl series so far, hints at near-future events including the reappearance of one of the Frontier Brains of the Kanto Battle Frontier.