This page offers a guide on how to complete Request 29: The Search for Bitter Leaves in Pokémon Legends: ARCEUS (PLA).
This quest is picked up from Shinon, who’s found on Canala Avenue. She’ll ask you to help with finding a plant for her medicine. Your first task, however, will be to ask Anise for more details. She can be found in a house nearby - and when you speak to her she’ll tell you to look for a Pokémon with three leaves coming out of its head.
How to Find a Petalil in ARCEUS
The Pokémon in question is a Petalil. You can find Petalils near Holm of Trials in Crimson Mirelands. To get to it, however, you’ll need to have access to the Basculegion mount that allows you to cross water.
There are a few Petalils around (we even spotted a randomly spawning Alpha Petalil), so if you miss a catch you can try again relatively easily.
Once you have a Petalil, head back to Anise and hand over the Pokémon. You’ll get x3 Fine Remedy and x5 Hopo Berry as a reward!