Fall

Fall, or Autumn, is an unlockable alteration in Super Mario World and its Game Boy Advance remake, Super Mario World: Super Mario Advance 2. This event changes the appearance of certain enemies, and it alters the color palette of the overworld map of Dinosaur Land to reflect the season from Spring. The theme is unlocked by completing Funky in the Special Zone in Super Mario World; in Super Mario World: Super Mario Advance 2, it is unlocked by completing all 96 exits.

Once these prerequisites are reached, the changes will take effect, preceded by a short cutscene in the GBA remake: Luigi is shown on a hot air balloon tossing masks down with a message stating "Mario and Luigi have found all of the goals. Congratulations!!! Now you can play a slightly different Dinosaur Land!" After this, Mario is seen running, where he jumps on a Koopa Troopa and takes its shell. A mask falls, and the Koopa walks to it and starts wearing it. The scene then cuts back to Luigi tossing masks, with Caped Mario attending Luigi. Super Koopas then appear, where they then carry a large sign saying "Congratulations," and Mario and Luigi flash their to the player.

Once Fall is activated, these changes cannot be reversed unless the save file is deleted and a new game is started.

In Super Mario-kun, in chapter 7 of volume 2, Mario gets shocked by an ON/OFF Switch and wakes up in a dimension where the Yoshi's Island is in Fall. Mario is stunned, seeing the strange enemies (especially the Koopas with his face) and a violent Yoshi. Enemies such as Boos, Monty Moles, and Pokeys also have fall variants here despite never having any in the original Super Mario World. After creating a giant shockwave with a Dragon Coin, Mario wakes up in the normal world, happy to see his brother and a gullible and always hungry Yoshi. In the next chapter, Mario, Luigi, and Yoshi face against a Jumping Pumpkin Plant, although in the normal world and not during the Fall.

Dinosaur Land
Fall causes Dinosaur Land to change color, with green objects becoming orange-brown and brown places becoming green. The water also becomes a teal color. Everywhere on the overworld map is affected, including places such as the Valley of Bowser. Although all of Dinosaur Land is changed, the visual appearance of the levels is not affected. The intro of Super Mario World: Super Mario Advance 2 will show Dinosaur Land in Fall at the start and end.

Enemies
Various enemies have their appearance changed in Fall. This change affects everywhere else in the game enemies appear in, including on menus and during the credits. These changes affect their aesthetics only.
 * Piranha Plants, Jumping Fire Piranha Plants, and Jumping Piranha Plants have jack-o'-lantern heads, and the latter are also known as Jumping Pumpkin Plants. While not an enemy, Beanstalks also undergo this change.
 * Bullet Bills become Pidgit projectiles and are also known as Pidgit Bills. In the original Super Mario World only, there is a quirk that causes the diagonal and vertical Bullet Bills of Vanilla Dome 4 to not change. They also visibly flap their wings in the GBA remake.
 * Koopa Troopas and Koopa Paratroopas wear Mario masks instead of Koopa shells, and the former are also known as Mask Koopas.
 * In some levels, this also causes any Green Koopa Troopas and their shells to become Yellow, and Red Koopa Troopas and their shells to become Blue. However, this doesn't apply to any standalone Koopas without Shells or any other Koopa Troopa species.
 * When Buzzy Beetles are inside their shell, they immediately come out without warning rather than shaking before they start coming out and moving again.
 * Goombas are yellow and wear sunglasses (Super Mario Advance 2 only).
 * Pokeys' segments turn into saws (Super Mario Advance 2 only).
 * The intro for Super Mario World: Super Mario Advance 2 and the title screen demo of Groovy change the enemies to their available Fall form, and the credits sequence of both games show enemies in their Fall form.

Trivia

 * In Super Mario World, Goomba has duplicate sprites meant for the Fall theme, albeit none for Para-Goomba. It is possible that it was meant to have a Fall-themed design before Super Mario Advance 2.
 * Among early assets for Super Mario World is a flower-headed, Toad-like creature, believed to be intended for the Fall theme of Piranha Plant, along with a Jumping Piranha Plant version resembling a Fire Flower.