Pokémon Legends: Arceus makes its premise pretty clear from the start: Complete the first-ever Pokédex. However, unlike previous games, you’re not just filling out a Pokédex — you’re creating one. As such, you’ll have to do a bit more legwork to fill out each Pokémon’s individual Pokédex entry than simply catching it. Here’s how to check the Pokédex registration requirements for each Pokémon in Legends: Arceus.
You can view registration requirements by opening up your Pokédex, which is done by pressing down on the directional pad. Once you open it up, you’ll be able to scroll through a list of Pokémon, which you can sort in a few different ways. After you find the Pokémon you’re looking to register, switch to the Research Tasks tab, which will show you a list of tasks you can perform to help register your Pokémon.
To register a Pokémon to your Pokédex, you have to get its Research Level, which is visible in the bottom-right corner of its Pokédex entry, to level 10. You can use this screen to easily check how close your Pokémon is to being registered. After you complete a Research Task, check in with Professor Laventon and your Pokémon’s Research level will increase by one for each task you’ve completed. In total, you’ll have to complete 10 tasks for each Pokémon, but you don’t have to do every single one; it’s up to you which ones you complete. Additionally, you can gain multiple Research Levels by repeating the same task, as certain tasks have multiple tiers, each of which counts as a single task when completed.