A brand-new costumed version of Snorlax has arrived in Pokemon GO, but how do you get nightcap Snorlax?
Currently, the only way to get Snorlax wearing a nightcap in Pokemon GO is to buy the Pokemon GO Plus + accessory and connect it to Pokemon GO.
Connecting the game to your Pokemon GO Plus+ device will give you the exclusive Catching Some Z’s Special Research that guarantees an encounter with a costumed Snorlax wearing a nightcap.
Despite this, Pokemon GO developer Niantic has confirmed that nightcap Snorlax will not be exclusive to just this Special Research. In the blog post announcing this costumed Pokemon, Niantic said:
“Trainers may have additional opportunities to encounter Snorlax wearing a nightcap in the future. Stay tuned!”
Pokemon GO Blog

Even if the exact date that nightcap Snorlax will be available for all players has not been available yet, this is encouraging news for players who don’t want to miss out on a costumed variant of an iconic ‘Mon!
The most likely time for nightcap Snorlax to return for every Pokemon trainer would be during a major in-game event, such as Pokemon GO Fest or Pokemon GO Tour. However, this summer’s GO Fest may be a bit too soon!

Can You Get Shiny Nightcap Snorlax?
Yes, the costumed Snorlax wearing a nightcap can be shiny, however, like all shinies, it is very rare.
The odds of nightcap Snorlax being shiny are around 0.2%, or 1 in 500. This is the standard shiny rate in Pokemon GO, and the same as the normal, non-costumed Snorlax.
Like the standard shiny version of Snorlax, shiny nightcap Snorlax is a deeper blue color compared to the regular version.
