Niantic has announced that Rivals’ Week will take place from Tuesday, April 13th, 2021, at 10:00 a.m. to Sunday, April 18th, 2021, at 8:00 p.m. local time in Pokémon GO. Therian Forme Landorus will be coming to five-star raids!

Note: On April 12th, 2021, Niantic removed the Team GO Rocket line from the press release.

Rivals’ Week brings rival Pokémon and competition! Plus, Therian Forme Landorus is coming to five-star raids!

Trainers, Some legends arise from the power of friendship—while others arise from fierce rivalries! The Season of Legends continues with Rivals’ Week, an event celebrating rivalries between Pokémon. Skrelp and Clauncher will be making their Pokémon GO debuts! Plus, Therian Forme Landorus will be appearing in five-star raids for the first time!

Date + Time
Tuesday, April 13, 2021, at 10:00 a.m. to Sunday, April 18, 2021, at 8:00 p.m. local time

Features

• Skrelp and Clauncher will be making their Pokémon GO debuts! They’ll be appearing in the wild, in raids, and in encounters after you complete Field Research tasks.
• Therian Forme Landorus is also making its Pokémon GO debut! Encounter the Abundance Pokémon in five-star raids.
• Enjoy the Rivals’ Week challenge in the Global Challenge Arena! All Trainers around the world can work together to win Raid Battles and unlock a 2× Catch Stardust bonus for the duration of the event!
• Pokémon known for their rivalries will be appearing more often in the wild, such as Hitmonchan, Hitmonlee, Makuhita, Meditite, Zangoose, Seviper, and more!
• The following Pokémon will be hatching from 5 km Eggs throughout the event: Machop, Tyrogue, Elekid, Magby, Makuhita, Meditite, Zangoose, and Seviper.
• Rivalries will continue in raids as well! Pokémon like Nidoqueen, Nidoking, Zangoose, Seviper, and more will be appearing in raids!
• Enjoy event-exclusive Field Research tasks that will lead to encounters with rival Pokémon, such as Skrelp and Clauncher, as well.
• Sources tell us that Team GO Rocket will be taking over PokéStops more often. Their balloons will also be appearing more frequently!

Please be aware of your surroundings and follow guidelines from local health authorities when playing Pokémon GO. Upcoming events are subject to change.

Source: https://pokemongolive.com/post/rivals-week-2021/?hl=en