Throughout its long history, the Pokémon anime has done many plotlines and story arcs, but not all of them reached a satisfactory conclusion. One of the most noteworthy plots to be suddenly dropped out of nowhere was the GS Ball plot, which provided the impetus for Ash to go on to the Orange Islands and then to Johto.
In the episode "Pallet Party Panic," right after Ash's loss in the Indigo League, Professor Oak asks that Pokémon's Orange Islands arc, Ash delivered the GS Ball to Professor Oak, but Oak wasn't able to make much progress in studying it, and instead asked Ash to take it to a Poké Ball expert named Kurt, who lived over in Johto. It takes a while, but Ash eventually reached Kurt and gave him the GS Ball... and after telling Oak it was delivered, it was never mentioned again.
The GS Ball was obviously meant to have some kind of greater significance, but whatever importance it was meant to have never came up, and viewers never got an answer to its mysteries. There are some things that fans can infer from Pokémon Crystal, however. There, the GS Ball is an item that could only be obtained through special in-person events; when taken to Kurt, he will examine it for a period of time before returning it. If players take the ball to the Ilex Forest shrine, placing it in the shrine will cause a Celebi to appear, allowing the player to catch the mythical Pokémon. Since the GS Ball is closely tied to Celebi in the games, it's reasonable to assume the same would be the case in the anime... but why was the plot dropped so suddenly?
The Pokémon Movies Were Prioritized Over the Anime
In a the first Pokémon movie had only been out for a few months, and it wasn't yet clear if Pokémon films would be a regular thing. However, by the time the GS Ball was written out of the show, the third movie's release was imminent, and a fourth was known to be on the way. Hidaka said that a decision was made to feature Celebi in the fourth film, eventually titled Pokémon 4Ever: Celebi, Voice of the Forest, and so to avoid complications, the GS Ball was written out before Celebi appeared in the series. Hidaka said they hoped fans would simply forget about the GS Ball... which didn't really happen since he was still getting questions about it eight years later.
This decision ultimately set the stage for Pokémon films to focus on mythicals from that point forward, keeping most of them from appearing in the series and forever altering what creatures the anime could and couldn't feature. Had the GS Ball arc played out differently, the Pokémon anime of today might've been very different indeed.
Source: Poké Beach
