Fall

Autumn is a special event present in Super Mario World and its remake Super Mario World: Super Mario Advance 2. This event changes the appearance of certain enemies, and alters the colour palette of the overworld map of Dinosaur Island to reflect the season of fall. Autumn is triggered by completing Funky in the Special World in Super Mario World, and attaining all 96 exits in the remake. Once these prerequisites are reached, a short cutscene is shown, at which point Autumn is unlocked. Once activated, these changes cannot be reversed.

Dinosaur Island
Autumn causes Dinosaur Island to change colour, with green coloured objects becoming brown and brown coloured places (such as Chocolate Island) becoming green. Everywhere on the overworld map is affected, including places such as the Valley of Bowser. Autumn will also affect non-living objects, such as the ground. Although all of Dinosaur Island is changed, the water on the overworld map remains the same colour, and the visual appearance of the levels is not affected. The intro of Super Mario Advance 2: Super Mario World will show Dinosaur Island in Autumn at the start and end.

Enemies
Various enemies have their appearance changed in Autumn. This change affects everywhere else in the game enemies appear in, in-game or on menus. This change only affects their look, thus they will continue to act the same. Galoombas will be coloured yellow and wear sunglasses, Pokey segments will turn into small Thwomps, Jumping Piranha Plants turn into Jumping Pumpkin Plants, Bullet Bills turn into Pidgit Bills, all Koopa Troopas become Mask Koopas, all Koopa Paratroopas become Para Mask Koopas, and all Kamikaze Koopas have their multicoloured shell transformed into a multicoloured Mario mask.

Additionally, for Mask Koopas, all Red and Green Koopas are replaced by Blue and Yellow Mask Koopas, and all Red and Green Shells (stray or on a Koopa) are replaced by Blue and Yellow Mario masks. Koopa Paratroopas are not affected by this colour change. In Super Mario World, diagonally shot Bullet Bills (such as the ones on Vanilla Dome 4) are not transformed into Pidgit Bills even after Autumn, and Pigit Bills do not flap their wings. These errors were fixed in the remake.

The intro for Super Mario World: Super Mario Advance 2 and the titlescreen demo of Groovy will change the enemies to their Autumn form (if they have one), and the ending of both games will show enemies in their Autumn form during the credits.

Trivia

 * It is incorrectly stated on Gnarly of Super Mario World: Super Mario Advance 2 that completing all the levels in the Special World would give the player a "special present". Although this is true in Super Mario World, it was changed in the remake.