Whether or not a Pokémon wearing clothes is actually a different Pokémon is debatable. After all, a new outfit doesn't actually change a Pokémon's stats, but Pokémon Go players are chasing Christmas Pikachu and its new Santa hat anyway.
The big Pokémon Go news from Monday was the introduction of some Gen 2 baby Pokémon that you can only hatch from eggs. So it's no wonder Pokémon Go fans are excited about catching Christmas Pikachu. Unlike those hatchlings, this is a new Pokémon that you can actually hunt down and capture.
How to catch Christmas Pikachu in Pokémon Go
Even Pokémon veterans are not absolutely sure how eggs function in Pokémon Go, and Niantic hasn't done much to clarify the issue. Many players think that the contents of an egg in Pokémon Go are predetermined, and early evidence seems to suggest that eggs obtained pre-update won't contain new Pokémon variations.
If that's true, any eggs you picked up prior to the Gen 2 update will not hatch Christmas Pikachu or any of the new Gen 2 Pokémon. You'll have to incubate all the eggs you had before the update hit and then start hatching brand new eggs gathered after Gen 2 arrived. Players have also speculated that Pikachu will no longer turn up in new eggs now that its baby form, Pichu, has been added to the game.
If you're stuck trying to capture Christmas Pikachu the old-fashioned way (with PokéBalls) you have one thing working to your advantage. Preliminary reports from the Silph Road suggest that all Pikachu in Pokémon Go are wearing the Santa hat right now. So at least you don't need to worry about finding Pikachu that aren't wearing the hat. Pikachu can be pretty rare for some Pokémon Go players to begin with.
Pokémon Go: Pikachu's Santa hat won't disappear when it evolves
Pikachu doesn't lose his holiday hat when he evolves into Raichu, but whether either Pokémon will be allowed to keep his Santa Claus accessory permanently remains to be seen. We'll find out after Dec. 29 when the Pokémon Go Christmas event ends and the special Pikachu can no longer be caught.
Niantic refers to Christmas Pikachu as a "limited edition" Pokémon, which does suggest that you keep these forever. How else would you demonstrate that you participated in the event?
More Pokémon Go hacks, tips and tricks
If you're really into the Pokémon Go holiday event, you may also want to check out Mic's Pokémon Go guides. Here's the new top 10 attackers list and the new top 20 rankings following the balance update, guides on post-update Chansey and Rhydon, everything you need to know about finding the long-awaited Pokémon Ditto, creating new PokéStops, how to maximize your chances of catching Pokémon and fresh information about how PokéStops distribute Pokémon eggs.