In Kingdom Hearts Final Mix, each World has three missions that reward the player with Gummi Blocks or blueprints upon completion. The missions require the player to reach a certain objective, like a certain score or number of enemies defeated, while sometimes limiting which Gummi Blocks can be used.
In Kingdom Hearts II, each Gummi Route has three Gummi Missions, which are unlocked after clearing the Gummi Route once. Mission 1 requires the player to collect as many medals before reaching the end of the stage, while Mission 2 counts the number of enemies defeated instead. Clearing both missions unlocks Mission 3, which requires the player to reach a high score. In Mission 3, players need to rotate the screen manually.
Kingdom Hearts II Final Mix adds an EX S Mission option to each of the three missions upon reaching an S-rank. EX S Missions are the same as the original, but have certain restrictions or requirements.
In Kingdom Hearts III, Gummi Missions are a list of goals that are shared between the three zones.
List of Gummi Missions
Kingdom Hearts Final Mix
Kingdom Hearts II
Kingdom Hearts III