Gastly, the Kanto gas Pokémon, can be found in the wild in Pokémon Go. Yes, Gastly can shine on Pokémon Go!
Although its shiny version is quite disappointing, Gengar is very meta when it comes to ghost and poison type moves. It's further boosted by its Mega form, which sits happily at the top of the DPS charts for poison-type attackers (at least for now).
What is Gastly's shine rate in Pokémon Go?
According to old research by the now-defunct website The Silph Road (via Wayback Machine), the shine rate of Pokémon on a typical day is about one in 500. Gastly is not a confirmed Pokémon to get a “permanent boost.” ” (meaning it is a rare spawn and therefore gets an improved shine rate).
What can I do to attract more shiny Pokémon?
Unfortunately, not much. It seems to be a coincidence. Shiny Pokémon catch rates are set by developer Niantic and usually only increase during special events like Community Days or Safari Zones, or in legendary raids. There are no consumable items that increase Shiny Pokémon rates.