Instructions
Head west out of Celadon. Use the Pokeflute to wake the sleeping Snorlax that blocks your path.
Defeat or capture Snorlax. This the last of two of this type of Pokemon in the game, so it will be your final chance to catch it for your team. Watch out for its "Yawn" attack, which will put you to sleep. Quickly bombard Snorlax with Ultra Balls in an attempt to capture it.
Stand on the square on which Snorlax was located after you defeat or catch it. Use ItemFinder to uncover Leftovers, an item that restores health.
Go inside the nearby guardhouse and climb the stairs to the second floor. Speak to a person here who will give you the Amulet Coin if you have captured at least 40 species of Pokemon. If you have yet to reach this number, revisit this location later to get the coin.