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When you arrive on Two Island, head south and use Cut on the tree to get a Revive. Stop at the Pokémon Center, then explore the island.

[edit] Game Corner

Talk to the man inside the Game Corner. The man is looking for his missing daughter, Lostelle, who is lost on Three Island. To get her, head over to Three Island.

[edit] Cape Brink

To the east of the Game Corner is Cape Brink. Fish for Poliwag. In the tall grass, you can find Oddish, Persian and Golduck.