Can Gastly be shiny in Pokemon GO? Yes! Gastly can be shiny!
Gastly's shiny form is somewhat more subtly different from its standard form than other shiny Pokemon. It has a purple body and periwinkle cloud around it in contrast to the black body and purple cloud of the standard version. It looks almost as if someone took the standard form and turned the brightness up. Pokemon later in the line are even more difficult to tell apart at first glance. Haunter's shiny and standard forms are almost the exact same color purple but the shiny form has a blue tongue instead of a pink one.
Can Gastly Be Shiny in Pokemon GO?
Gengar continues the trend with the shiny form being a de-saturated, almost grey, shade of purple, as compared to the standard form's slightly more vibrant purple. The Shiny form really starts to shine in Gengar's mega form. Shiny Mega Gengar is stark white with grey eyes and pink under lighting and with the mega evolution update on its way, you can definitely expect to see this form in Pokemon GO.
How to Catch Shiny Gastly
As with all shinies, it's mostly down to the random number generation, but there are some things you can do to improve your chances. Gastly is a ghost and poison type, so it will show up more frequently during cloudy or foggy weather. Since the Gengar line is so popular, Gastly is also a common fixture for community events like Sunday's Gastly themed community day, and the yearly Halloween events.