Catch Missing No.
# Go to Viridian City and talk to the old man located in the north. When he asks if you are in a hurry, say "No".
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2
After watching the demonstration, immediately Fly to Cinnabar Island. Flying to Fuchsia City also works.
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3
Surf to the east coast of Cinnabar Island. Or, if you flew to Fuchsia City, Surf south and west until you get to the Seafoam Islands.
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4
Once you get to the Cinnabar Island, Surf along the coastlines.
At the same time what ever item is in your 6th item slot will multiple by 99.