There are  stories of people hunting down Pokémon on their office desks, in hospital rooms, and even in bathrooms. One teenage girl even found a dead body while looking for Pokémon. And police in Missouri claimed that four suspected robbers lured in victims with the possibility of Pokémon. Vox has reported.

What the hell is going on?

Well, after a few years lying relatively low, Pokémon is making a bit of a comeback. According to Vox, the Nintendo-owned franchise, which exploded in popularity in the late 1990s, is again taking America by storm — this time through Pokémon Go, its biggest entry into the mobile space, now available for a free download onAndroid and iOS. It’s so popular that it’s on the verge of overtakingTwitter in terms of daily active users on Android.

In simple terms, Pokémon Go uses your phone’s GPS and clock to detect where and when you are in the game and make Pokémon “appear” around you (on your phone screen) so you can go and catch them. As you move around, different and more types of Pokémon will appear depending on where you are and what time it is. The idea is to encourage you to travel around the real world to catch Pokémon in the game. (This combination of a game and the real world interacting is known as “augmented reality.” More on that later.)