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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.

How about a nice leek in this trying time?
This page or section details content from the July 2020 Nintendo Leak (AKA: "Gigaleak").
Check the July 2020 Nintendo Leak category for more pages also sourced from this material.

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. The prototypes also shows a unique HUD.

To do:
  • There are 4 files in the gigaleak, labeled ys_rom_0, ys_rom_1, ys_rom_2, and ys_rom_3, located in both the Ver0\sfc folder as well as in Ver2\sfc. Combining these files will yield unique, functioning ROMs, but it is undetermined if they predate ys_main_db.
  • .ys_rom3.bin (not to be confused with ys_rom_3.bin) appears to be the fourth quarter of an otherwise missing build of the game. Research is needed to determine its uniqueness.


Yoshi's Island (ys romX 0) Titlescreen.png
Dated December 6, 1994 and rather different from the final game, including the presence of Super Mario World music and sound effects as placeholders.
Yoshi's Island (ys rom 0 D) Title screen.png
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. To fix a header, set the byte at 0x7FBD to 05, and set the bytes starting at 0x7FD5 to 20 15 0B 00 00. Build dates can sometimes be found at 0x7FA0 in the HH-MM-DD-hh-mm format.


Dated December 19, 1994. Mostly the same as ys_rom_0_D.bin 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.


Dated June 26, 1995. A near-final build with a few minor code differences. In addition, the final game's debug features are enabled by default.

This build has no internal ROM header at all and requires a fix.

Graphical Differences

Proto Final
Early POW.png Final POW.png

The P is different, the right end of the W is higher, and the shading is different.

Proto Final
Early POW small icon.png Final POW small icon.png

The small POW Block is blue (akin to its appearance in Mario Bros. and more modern games) and has an extra shadow that was removed from the final.


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.bin, except with the final game's debug features also enabled. Requires a header fix.


Combining the 4 512kb bin files and patching the header yields working ROMs. This applies to both the ones found in Ver0\sfc, as well as Ver2\sfc. Differences are present when compared to other ROMs in hex editors. The ROM from Ver0 is also dated June 26, 1995, strangely, whereas the one from Ver2 has a date of Oct 2, 1995.


Included in the leak are ROMs that appear to contain editors allowing for map and level creation and play testing. In order to run these, an emulator with SFX-DOS support is required, such as this branch of bsnes-plus. The mouse should be configured to be in controller Slot 2. Most of these tools require a header fix, as described above. Set the byte at 0x7FBD to 07 (1Mbit of Expansion RAM) instead of 05 to fix graphical corruptions.

To do:
Add more details about the functionality, usage, and differences between the various editor ROMs. In addition, investigate and compare graphics, sprites, etc.


Upon booting this level editor, there are two choices: ENMY DATA SET and BG EDIT. No header fix is required. The first allows for placement of enemies on the map, and the second choice allows for editing of map tiles.

Ystool-Main Menu.png
Ystool-ENMY DATA SET.png
Ystool-BG EDIT.png


Dated December 23, 1994. Seems to be pretty close to ystool.hex in functionality.

Found within the sprite files of the Level Select icons were found sprite differences and even unpublished icons!

World 2

Early (World 2-2) Proto (World 2-2)
Early W2-2.png Late W2-2.png

World 4-6 icon ended up being placed on World 2-2.

Early (World 2-3) Proto (World 2-3)
Early W2-3.png Late W2-3.png

The icon has been mirrored and Yoshi's head is a little different.

Early (World 2-8) Proto (World 2-8)
Early W2-8.png Late W2-8.png

Apparently the Naval Piranha icon has been replaced by Roger the Potted Ghost which makes sense with what is shown on the stage in ys_rom_0_D!

World 4

Early (World 4-1) Proto (World 4-1)
Early W4-1.png Late W4-1.png

This icon makes more sense with the stage seen in ys_rom_0_D! Besides that it, resembles the final World 3-1 icon.

Early (World 4-2) Proto (World 4-2)
Early W4-2.png Late W4-2.png

Leaves were added, bringing it closer to the final version.

Early (World 4-3) Proto (World 4-3)
Early W-4-3.png Late W-4-3.png

The Lunge Fish icon was moved, while a Blue Piranha Plant remained in its place.

Early (World 4-4) Proto (World 4-4)
Early W-4-4.png Late W-4-4.png

The background is more detailed.

Early (World 4-5) Proto (World 4-5)
Early W-4-5.png Late W-4-5.png

The Lunge Fish icon was moved to World 4-5, and Yoshi is not being swallowed by Lunge Fish. This icon also makes more sense with the same level in ys_rom_0_D!

Early (World 4-6) Proto (World 4-6) Correct Palette
Early W-4-6.png Late W-4-6.png Late W-4-6 Fixed.png

This icon uses the incorrect palette, and is very similar to the final's World 3-6 icon.

Early (World 4-7) Proto (World 4-7)
Early W-4-7.png Late W-4-7.png

The original World 6-6 icon ended up being used for World 4-7 instead.

Early (World 4-8) Proto (World 4-8)
Early W-4-8.png Late W-4-8.png

The Naval Piranha icon has more details and has been changed for World 4-8.

World 6

Early (World 6-1) Proto (World 6-1)
Early W-6-1.png Late W-6-1.png

The background has fire added, with more details added and Boo Guy being redrawn.

Early (World 6-2) Proto (World 6-2)
Early W-6-2.png Late W-6-2.png

Yoshi is orange, and the background has been darkened.

Early (World 6-4) Proto (World 6-4)
Early W-6-4.png Late W-6-4.png

The icon has completely changed to something more three dimensional!

Early (World 6-6) Proto (World 6-6)
Early W-6-6.png Late W-6-6.png

A new icon was made, showing Little Mouse with a skull mask.


Mostly the same as yst_rom.bin and ystool.hex, but with a few minor differences. Setting the byte at 0x7FBD to 03 causes a 3rd option, "UNDO BACK-UP", to appear.

Yst rom 0 - Main Menu.png


This ROM appears to be an editor for the main overworld Mode 7 map. This tool allows you to place objects on and around the island, save/load maps, as well as manually walking Yoshi around the island.


  • Set Mouse to Controller Port 2.
  • Click on "MAP A" through "H" to change the map. Only MAPs A through D seem to have working graphics.
  • Click on "UNIT NO." to browse through the objects (left click a digit to increase it from 0-F, or right click to go backwards), then click the object in the black area to select it, then place it on the map.
  • Use the D-Pad to pan the map around.
  • Click the "MOVE" button to change modes to move placed objects, CLR to delete.
  • Click the "MAP" button to walk Yoshi around the Island using the D-Pad. To get back to the editor, press the right and left mouse button at the same time.
  • Click "P.SET" to enter "MAP POINT DATA SET MODE". This allows one to set the locations of each World on the map, indicated by yellow star sprites.
  • Click "MENU" to display a list of all World points that have been placed on the maps. From here, click "DATA" to bring up a settings menu. Clicking "MAP" in this menu will enter "PLAYER MOVE DATA SET MODE", allowing one to define the route of the Worlds. Click "TEST" to show Yoshi walk to each world, similar to how it's done in the final game, when beating a world and progressing to the next.
  • Click "FILE" to save, load, and manage .mpd and .pdt files on the floppy disk.
Ysm rom-Editor View.png
MENU view FILE view
Ysm rom-Menu View.png
Ysm rom 0-FILE menu.png

This gif shows all available objects placed onto the map. Most of the Yoshi animation frames were omitted in this gif:

Ysm-rom 0-sprites01-79.gif

Animation frames: White puff = 1C - 22, Flying bird = 23 - 2A, Yoshi = 2B - 5A, Explosion = 74 - 79


Combining the 4 ysm_rom*.bin files (0-3) produces a bootable ROM. Mostly the same as ysm_rom_0.bin, but upon booting, it displays a man in a brown suit, as opposed to baby Mario. There are less objects available to place than in ysm_rom_0.bin, starting at "UNIT NO." 6B. A comparison is depicted below.

ysm_rom_0.bin ysm_rom*.bin
Ysm rom 0 - Editor View.png
Ysm rom - Editor View.png