If you’re a Pokémon fan who frequents YouTube and Twitch, you’ve probably seen some big creators playing something called PokeRogue. This roguelite title isn’t an official Pokémon game but it is very quickly taking the internet by storm—but what exactly is PokeRogue and why has it become such a hit?

PokeRogue is a unique take on the classic Pokémon formula developed by fans, for fans outside of the usual ROM hack style that the community has become accustomed to seeing. It takes some of the best parts of the roguelite genre to pair with Pokémon’s iconic creatures, putting a focus on battles and challenging players to build dynamic teams to take on challenges completely different to that of the main series.