The Armored Mewtwo event has started bringing a clone Pokemon with it to Pokemon Go. You can find these Pokemon featured in Four Star Raids, and you can try to locate a Pikachu clone by taking photos of your Pokemon. Other Pokémon have come to the event, and you can now capture Pikachu, Eevee, Squirtle, Charmander, and Bulbasaur, who are wearing party hats.
There are different ways to capture these Pokémon. The Pikachu Party Hat and Pokemon Eevee are probably the easiest as you can find them freely roaming the world and you can see them roaming your area. You should be able to see their party hats on their heads in the outside world, which makes it a lot easier. You also have the option of being a shiny version of the Pokémon.
If you are looking for the Charmander, Squirtle and Bulbasaur party hat, you have to work a bit more for these. You can find them in seven-kilometer eggs, which means you have to free up incubator space to attempt to hatch them. Additionally, they should appear as One Star Raids. You can tell the rating of a Pokémon raid by the number of symbols above it when you click on it from the world, and it should only have one icon. You can also find them as their shiny version.
To acquire a Seven Kilometer Egg, you must receive a gift from a friend on your Friends list. Make sure your friends send you as many gifs as possible throughout the event, and send them gifts in return to give them a chance to try and hatch one with a party hat. The Armored Mewtwo event runs from February 25 to March 2.