Andra thinks Mr. Mimes are fairly strange, and he wants your help in finding out why. In Pokémon Legends: Arceus, you’re tasked with finding out why they pretend to be in invisible boxes.
To pick up the request, head to Jubilife Village and talk to Andra, who is standing by the river that goes through town. He’ll tell you that this particular Mr. Mime is acting stranger than most and wants help in finding out why.
Once you begin the request and find Mr. Mime, you’ll be unable to reach the Pokémon from the front, since it has an invisible wall that you cannot pass through in front of it. You’ll have to go all the way around the other side of the buildings in order to approach it from behind and interact with it. You don’t have to sneak up behind it: it won’t hear you. Once you interact with it, it will act surprised and run away from you.
Next, you’ll have to find Mr. Mime a second time. Just like before, you can’t pass through to get it from the front, so you’ll have to find another way around to interact with it from behind.
This part can be a little tricky, so you’ll want to approach Mr. Mime from the left side (his right side). You’ll want to start very far to the left by running past the sweet treats vendor, around the building behind him, and then start running along the mountain side to avoid his invisible wall. Once you get close to it, you’ll hit a wall right next to him. Run to the right a bit to get around that invisible wall and interact with it from the side.
In order to approach him the third time, start by running to the left from where Andra is standing. Run to the ladder, then run right and zig-zag in order to get around the invisible wall. After that, you’ll have completed the quest.