A lot is happening in Pokémon GO this April, including events based on spring, rivals, friendship, and more. These releases will bring forth the release of some brand new Pokémon appearing in the game for the first time.
The full details for April 2021 were announced on the official Pokémon GO blog:
Team GO Rocket Timed Research: From Thursday, April 1, 2021, at 12:00 a.m. to Thursday, April 8, 2021, at 11:59 p.m. local time, be sure to complete Timed Research to get a Super Rocket Radar, which you can use to battle Giovanni!
This was expected, as it was already announced that we'd be cycling through the Shadow Birds again. This time, Giovanni battles completed in April will reward Shadow Zapdos encounters. One major change, though, is that this Team GO Rocket questline will be Timed Research rather than Special Research so be sure to complete the tasks while they're still active.
Spring into Spring: From Sunday, April 4, 2021, to Thursday, April 8, 2021, you can look forward to a spring-themed event! Look out for Chansey, Blissey, and Happiny wearing flower crowns, as well as other spring- and Egg-themed surprises!
No word on the full details, but this is the first time we're getting new costumed Pokémon since January. Personally, I hope we see previous Easter-themed and Spring-themed Pokémon return. I know everyone was tired of Flower Crown Eevee for a while, but I'd certainly take one if it's spawning in the wild.
Rivals' Week: From Tuesday, April 13, 2021, to Sunday, April 18, 2021, Pokémon that are rivals will be featured, including some Pokémon making their Pokémon GO debut!
Pokémon I'd expect to see boosted are the rival pairs of Zangoose and Seviper along with Heatmor and Durant. I couldn't imagine what species will arrive in this event. Niantic has been focusing a lot on the release of Unova Pokémon rather than continuing the Kalos rollout. Unreleased Unova species include Zorua (and Zoroark), Mienfoo (and Mienshao), Druddigon, and Larvesta (and Volcarona).
Sustainability Week: From Tuesday, April 20, 2021 to Sunday, April 25, 2021, you can look forward to a sustainability-themed event! Pokémon like Grimer, Trubbish, and more will be appearing more often in the wild, and it's up to all of us to catch them!
Could this be our Trubbish Shiny release>?
Friendship Day: On Saturday, April 24, 2021, celebrate friendship with a brand-new event!
What a perfect day to release Sylveon…
April will end with a snappy event that will continue into May, so keep a lookout for more details later in April!
Snappy makes me think of GO Snapshot. Maybe a new species will start photobombing. Imagine it's Kecleon? It has to happen at some point!