Where Onix is hiding

Onix is in the Withered Wasteland, the first area in Pokémon Pokopia. Head northwest from the Pokémon Center toward the gate to Rocky Ridges. You will find Onix trapped behind a wall of hard rock inside a cave you cannot enter yet.

Before you can reach it

Two story requests stand between you and Onix: Investigate the Cave and Yawn Up a Storm. Work through both. Completing them triggers rainfall in the Wasteland, which softens the rocks around Onix. Once the rocks are soft, use Rock Smash on the wall to free it.

If you have not triggered rain yet, go back to the Slowpoke request. Build a Seaside Tall Grass habitat by placing four grass patches next to the ocean in the Eastern Grove. That raises humidity and starts the rain.

Getting Onix to stay

Freeing Onix is not enough. It needs a home, specifically the Smooth Tall Grass habitat. That habitat takes four Dry Tall Grass patches and one Smooth Rock, placed in any layout.

Finding the Smooth Rock: After you free Onix, go deeper into the cave past the small waterfall and pool. Look for a blocked passageway that leads back to the Pokémon Center. Just outside the entry to that passage, pick up the Poké Ball on the ground. It contains the Smooth Rock.

Making Dry Tall Grass: Use the Leafage move on any patch of unwatered soil to grow Dry Tall Grass. You need four patches. If rain keeps wetting the soil, build the habitat inside the cave instead. Rain does not reach in there, so the grass stays dry.

Placing the habitat

Open the Build Queue and add four Dry Tall Grass patches and one Smooth Rock. Place them anywhere near the cave entrance in the northwest of the Wasteland. Onix moves in once you place the habitat.

Check the Habitat Dex after Onix arrives to see its specialty and what items it brings you over time.