The mobile gaming world today is a huge moneymaker, with in-app purchases generating way too much money in revenue. Even popular desktop games like Fortnite and PUBG are making their way to phones to get a piece of the pie. These types of games often have events, and the Play Store's 'My apps & games' page can now show notices for them.
The feature is pretty straightforward: it gives a short summary of the event in question in order to encourage those who have it installed to hit 'Open.' In this instance, there's some sort of summoning event for the game Fire Emblem Heroes. The feature is definitely primarily meant for games, though other apps may also be able to take advantage of it.
Let us know if you've seen this for any other apps/games, as this is our first time spotting it.