Follow the stops in order: each area opens up as the main missions progress. Each Pokémon is listed in the first area where you can find it. Tap a row to check it off. Evolves into shows later stages and how they evolve.
Shiny Charm: catching isn't enough here. Every non-Mythical Pokémon in the Hisui Pokédex needs Research Level 10 (from its research tasks), then you report to Professor Laventon. Use this route to catch them all first.
Spiritomb wisps
Request 22 asks you to gather 107 wisps scattered around Hisui. They glow and are easiest to see at night. Once you have them all, visit Vessa at the Shrouded Ruins in the Crimson Mirelands at night to battle and catch Spiritomb (level 60). Every wisp is a one-time pickup.
Unown
After your first trip to the Solaceon Ruins, the Unown Notes in your Pokédex start giving clues to 28 Unown forms hidden around Hisui. Catch each one where it appears; once you have all 28, more start spawning in the Solaceon Ruins.