Substitute Doll

The Substitute Doll is an item that appears in the Pokémon series. Although this item appears in the game's files, it has never officially been implemented into Pokémon GO.

Description
The Substitute Doll is an item often associated with the move Substitute (which currently does not exist in Pokémon GO). When the move is used, the Pokémon will temporarily retreat and the doll will be put in its place. The doll appears to be a green dinosaur-like stuffed animal with two closed eyes and a smiling mouth.

2017 model glitch
In late March of 2017, a large version of this item's model began appearing over Gyms in place of whatever Pokémon had most recently been assigned to said gym. It was believed by many that this would turn out to be a sneak-peak into a future update for gyms, but this would not end up being the case. Reportedly, the glitch was occurring because the model was being used as a default for when Pokémon failed to load at the top of the gym.

Trivia

 * Because of Pokémon GO's battle system, it is very unlikely that this item will be implemented as a part of the move Substitute.
 * It is currently unconfirmed whether or not the model still exists in the game's files.
 * The model was first discovered in the Apple Watch version of the game by a Reddit user in late January of 2017.