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Proto:Super Mario World 2: Yoshi's Island

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This page details one or more prototype versions of Super Mario World 2: Yoshi's Island.

Several prototypes of Super Mario World 2: Yoshi's Island were leaked alongside source code on July 24, 2020. The same leak also included an unreleased game called Super Donkey, which featured various elements that ended up later being used in Yoshi's Island.


Dated December 6, 1994 and rather different from the final game, including the presence of Super Mario World music and sound effects as placeholders.
Dated December 19, 1994. Largely the same as ys_romX_0, but there are some new added elements, such as the final's music and sound effects.

Other Builds

A few other builds with minor differences were also present in the leak. Most of these require changes to the internal ROM header in order to be emulated correctly.


Mostly the same as ys_rom_0_D but with a few minor code differences, including a slight change to how the aiming cursor moves when you first begin to throw an egg: Specifically, when charging up a throw, the cursor stays fixed in place instead of starting at a low angle and moving upward.


A near-final build with a few minor unknown code differences. In addition, the final game's debug features are enabled by default.

This build has no internal ROM header at all. To get it bootable in emulators, change the byte at 0x7FBD to 05 and the bytes at 0x7FD5 to 20 15 0B 00 00.


Identical to the final build, but with some additional debugging features accessible through Controller 2 during gameplay:

  • Pressing A/B/X/Y/Select toggles graphic layers on/off.
  • Pressing L toggles the background color gradient on/off.
  • When the background gradient is disabled, pressing R cycles through a few solid background colors.

The first time you start a level, all graphic layers are disabled by default for some reason, so you'll need to use this feature to actually make the game playable.


Same as ys_rom_16_0, except with the final game's debug features also enabled.