Gastly, the Gas Pokémon from Kanto, is found in the wild Pokémon Go. Yes, Gastly can be shiny Pokémon Go!
Although his Shiny version is pretty disappointing, Gengar is very meta when it comes to Ghost and Poison-type moves. Pushing it even further is its Mega form, which (at least for now) sits happily at the top of the DPS charts for poison attackers.
What is the shiny rate for Gastly in Pokémon Go?
According to old research from the now-defunct website The Silph Road (via Wayback machine), the shiny rate for Pokémon on a normal day is approximately one in 500. Gastly is not a confirmed Pokémon that receives a “permaboost” (meaning that it is a rare spawn and therefore receives an increased shiny rate).
What can I do to attract more shiny Pokémon?
Unfortunately not much. It seems to be a coincidence. Catch rates for Shiny Pokémon are set by developer Niantic and are typically only increased during special events such as Community Days or Safari Zones, or during Legendary Raids. There are no consumable items that increase the rate of Shiny Pokémon.