After you report to Cyllene, you agree to help Mai investigate a massive mass outbreak in the Obsidian Fieldlands.

The Request

After you complete A New Anomaly, you can talk to Mai near the Front Gate of Jubilife Village. There will be a cutscene. You can close the map to proceed.

Investigate

Go to one of the question marks on the map and catch or defeat pokémon there. Keep catching or defeating the pokémon at the location of the outbreak, and a message will appear when you have cleared all the pokémon away. They may be replaced with a new horde of evolved forms or alpha forms of the pokémon at the same location. If you take too long and the massive mass outbreak ends, go back to Jubilife Village, then go to any area outside of the village, and keep going back and forth until another massive mass outbreak occurs.

Report to Mai

After you have cleared away all the pokémon in three massive mass outbreaks, talk to Mai at Heights Camp. You will get 30 Tumblestone, 40 Iron Chunks, and 20 Smoke Bombs.