Fall

Autumn is a special event in Super Mario World and its remake Super Mario World: Super Mario Advance 2. This event causes the appearance of Dinosaur Island to change color and certain enemies to change their appearance. This event is triggered by completing Funky in the Special World in Super Mario World, and attaining all 96 exits in the remake.

Upon these prerequisites being attained, a short cutscene is shown, and at which point Autumn is triggered. Upon being triggered, Autumn cannot be reversed.

Dinosaur Island
Autumn causes Dinosaur Island to change color, green coloured objects becoming brown, and brown colored places (such as Chocolate Island) becoming green. Everywhere on the overworld map is effected, including places such as Valley of Bowser. Autumn will also effect non living objects, such as ground, and not just plants. Levels are not changed or effected at all. The intro of Super Mario Advance 2: Super Mario World will show Dinosaur Island in Autumn at the start and end of the intro. Although all of Dinosaur Island is changed, the water remains the same color.

Enemies
Various enemies have their appearance changed in Autumn. This change only effects their appearance, they continue to act the same. Kuribons will be colored 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 multicolored shell transformed into a multicolored 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 effected by this color change. Although this change just effects enemies, this change also effects everywhere else in the game enemies appears, in-game or on menus. 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 showing of most enemies in the game.

Although diagonally shot Bullet Bills (such as the ones on Vanilla Dome 4) were not transformed into Pidgit Bills even after Autumn, and Pidgit Bills didn't flap their wings, these were fixed in the remake.

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.