Certain WiiU and 3DS games have a link with Miiverse, Nintendo’s Twitter before it closed 2017, you could post… posts from the game your playing when you beat a specific level or complete an achivement. You could also see and interact with other peoples posts ingame, in Super Mario 3D World for example you would see other players avatars on the world map, see their Miiverse posts and interact with them. It merged ingame worlds with Miiverse extremely well, making it feel like you were part of a tight not community Good Vibes Gaming did a very good video about Pretendo as a whole good watch if your interested