What was in the gs ball Pokemon?

Answer 1

'....When Professor Oak couldn't do anything with it, Ash was once again asked to deliver it to Kurt, a Poké Ball researcher and manufacturer living in Johto's Azalea Town. It presumably still resides there to this day, and its purpose was, before 2008, unknown. In an interview with Masamitsu Hidaka in 2008 by the webmaster of PokéBeach, it was explained that the GS Ball was meant to contain a Celebi that was to be the star of a large arc of the Johto saga. However, it was decided that Celebi would be the star of the fourth movie, so the story arc was viewed as redundant and shelved. The ball was left with Kurt with the hopes that viewers would eventually forget about it.'

In other words, it was supposed to contain a Celebi, but was instead tossed out in hopes that we would ignore it's existence

Answer 2

The GS Ball, also named the Gold and Silver Ball, was a special item in the Pokemon anime which Ash and his friends needed to deliver to Professor Ivy. The item itself was a mystery and it is unknown what was discovered about it. However, it is unlikely to have contained a Pokemon.

In Pokemon Gold, Silver and Crystal, the GS Ball was an item received in a special sort of Nintendo Event. The item was transfered from a mobile phone (or cell phone) to a player's game to activate an event. When placed at the foot of the Ilex Forest Shrine, the GS Ball would cause Celebi to appear - engaging in a battle with the player and allowing for its capture. In this circumstance, the GS Ball still contains nothing but acts as a luring item.

It was speculated that the GS Ball contained Celebi, but this is not so.