After a mix-up that kicked off the event early, Niantic has reconfirmed that tomorrow is Marill Limited Research Day in Pokémon GO, so perhaps you can make plans to chase a green Shiny circle-mouse on the way to get flowers for your mother. From 8 AM – 10 PM tomorrow, Sunday, May 9th, you will be able to complete Field Research and Timed Research that can potentially lead to a Shiny Maril encounter.
Here are the full details for Marill Limited Research Day straight from the Pokémon GO blog:
As Fairy-type Pokémon continue to appear more often in the wild during the Luminous Legends X event, you can look forward to a Limited Research event featuring the Water- and Fairy-type Pokémon Marill! On Sunday, May 9, 2021, from 8:00 a.m. to 10:00 p.m. local time, you can complete event-exclusive Timed Research tasks that lead to encounters with Marill. If you're lucky, you might even encounter a Shiny Marill! You'll also be able to complete event-exclusive Field Research tasks that lead to encounters with Marill.
Now, over the years, Limited Research Days in Pokémon GO have dramatically changed. The final one done in the original style, which was purely Field Research-based, was Minccino Limited Research Day in pre-COVID 2020. The lockdown led to adjustments to these events, with Timed Research added as the primary way to play the event. Since then, the events have been slightly less predictable with the structure of the Timed Research and the Shiny rates, which have historically been boosted but seem to fluctuate a bit now.
Personally, I predict quite a high Shiny rate for Marill tomorrow, as Niantic isn't exactly keeping Marill as a rare Shiny in Pokémon GO. It has, in fact, already seen a day similar to this event back in 2020 for GO Battle Day: Marill. That event tasked players with completing PVP battles in GO Battle League, which would lead to, if the battle was won, a Marill encounter. The Shiny rate during that day was highly boosted as well. Note that we can't use the early research mistakenly sent out on Friday to judge the Shiny rate, as the boosted Shiny rate will likely be in effect only during the correct time.
Best of luck to everyone playing this event in Pokémon GO! Niantic has said that those who have started the initial Timed Research that was sent too early will restart, but neither those in the middle of progress nor those who completed the early research will lose the Pokémon they caught or the XP they earned.