The 15 Puzzle is a secret minigame in the original Final Fantasy that can be played after having obtained the ship. It exists in nearly every version.

• NES/WonderSwan Color: Press A & B together 55 times.
• Origins: Press X & O together 55 times.
• Advance: Press A & B together 22 times.
• 20th Anniversary: Press X & O together 22 times.
• iOS/Windows Phone: Press the screen with one finger and touch the screen 22 times while holding.
• Android: No way to access the puzzle game.

In the puzzle, the player must organize 15 squares into numerical order by sliding the squares. After solving the puzzle, the player receives prizes, such as gil and items.

In the original NES version, the reward for completing the puzzle is simply 100 gil. From the WonderSwan Color version onwards, the prizes are better, including:

• 1st place: 10,000 gil
• 2nd place: 5,000 gil
• 3rd place: 2,000 gil
• Under 2 minutes: Antidote, Gold Needle, Potion
• Under 4 minutes: Antidote, Potion
• Under 6 minutes: Potion

In the Dawn of Souls and 20th Anniversary versions, the prizes are again improved:

• 1st place: Megalixir
• 2nd place: Elixir, Remedy, Hermes' Shoes, Emergency Exit, Turbo Ether
• 3rd place: Spider's Silk, White Fang, White Curtain, Red Fang, Red Curtain, Blue Fang, Blue Curtain, Vampire's Fang, Cockatrice Claw
• Just finishing: 100 gil, Potion, Antidote, Gold Needle, Ether, Phoenix Down, Eye Drops, Echo Grass

Earning 1st, 2nd or 3rd place also rewards a "just finishing" prize.

The times to complete the puzzle are as follows:

• 1st place: 0:30.00 or less
• 2nd place: 0:30.00–1:00.00
• 3rd place: 1:00.00–2:00.00

In the pixel remaster version, there is no timer, and all prizes are removed. Completing the puzzle does, however, grant an achievement.