Legendary Event: Give and Take
The new Give and Take legendary event will begin on February 10, 2021. In this event, the Legendary Pokémon Xerneas and Yveltal will appear. Each forms a sync pair with a Trainer who might be a little unexpected, so try to guess who their partners might be. You’ll be able to add one sync pair from the event to your team. The other will appear in the sync pair scout. Just like with returning legendary events, from this event on, you can get 20 Custom ★ Power-Ups for the sync pair that joins your team—and raise their move level to 5★.
Source: Official Pokémon Masters EX site