Directly to you from Twitter:
The brand-new event, Tap Battle: Illusory Dungeon, has begun! Tap with accurate timing to take down enemies with 4 Heroes of your choosing and dive into the depths of this battle game. #FEHeroes pic.twitter.com/echCa2MdAc— Nintendo of America (@NintendoAmerica) February 9, 2018
…Wanna play? Buy a 3DS.
That being said, click on Fire Emblem Heroes for everything you need to know about the game. 😀