While Pokemon Legends: Arceus isn't open-world, it is more open-ended than most other Pokemon games. Players are generally free to tackle the game's objectives, outside the story, whenever they want to. The Pokedex is something that players can tackle at any time, with some exceptions. Players will need to progress to certain ranks on the Pokedex to be allowed access to the next area. However, one Pokemon Legends: Arceus player took that open-ended objective to the extreme in the first area of the game.