Sprite Issues

Why doesn't my boss battle function correctly?: Bosses are some of the most complex sprites in the game, and require quite a lot of experimentation to edit. First of all, many boss settings are world-specific. If you use a boss in any world other than the one it originally appeared in, without changing these world-specific settings, your battle will likely be glitched. To relocate bosses to different worlds, you will need to use a hex-editor to swap certain setting bytes.

Below is a tutorial on how to make these hex edits by Zeldara109 and Mattrizzle.

Tutorial: Show/Hide
Please note that bosses originally used as x-4/x-8 bosses still act like x-4/x-8 bosses, regardless of the actual level they appear in. For example, if you use Burt the Bashful in World 5, you'll need to modify the setting for 5-4's boss, even if you used Burt the Bashful in 5-8, 5-1, 5-Extra, or somewhere else.

These are the settings you'll need to modify (colored for easier reference) (my comments are in purple):

Originally posted by Mattrizzle
The values go in this order: 1-4 boss, 1-8 boss, 2-4 boss, and so on through the 6-8 boss.

65C60 Text pointers to Kamek's speech before each boss battle(each pointer is two bytes) (This can be left unchanged.)

The following 7 tables contain the non-header settings for Kamek's magic spells in each boss battle:

Each of these tables are 1 byte per boss battle...
65C76-65C81 [02 02 02 02 04 04 02 04 02 04 04 04] Unknown 1 (02=Layer 2, 04=Layer 3)

65C82-65C8D [35 35 35 35 33 33 35 B3 35 33 33 33] Unknown 2 (35=Layer 2, 33=Layer 3, B3=Layer 3. color inverted)

65C8E-65C99 [04 04 04 04 01 01 04 01 04 01 01 01] Unknown 3 (04=Layer 2, 01=Layer 3)

...and these are 2 bytes per boss battle:
65C9A-65CB1 [D8 00 D8 00 D8 00 D8 00 FA 00 FA 00 D8 00 FA 00 D8 00 FA 00 FA 00 FA 00] 00D8=Layer 2, 00FA=Layer 3

65CB2-65CC9 [00 3E 00 3E 00 3E 00 3E 00 36 00 36 00 3E 00 36 00 3E 00 36 00 36 00 36] VRAM upload location for magic tilemap (3E00=Layer 2, 3600=Layer 3)

65CCA-65CE1 [1F 61 DF 22 00 7F EC 23 1F 61 DF 22 00 7F 13 5C 1F 61 DF 22 00 7F EC 23] Color of Kamek's first magic spell (Changing this is optional; you can also experiment with different values)

65CE2-65CF9 [DF 22 00 7F EC 23 00 7F 00 7F EC 23 1F 61 20 5D EC 23 1F 61 DF 22 1F 61] Color of Kamek's second magic spell (Changing this is optional; you can also experiment with different values)

65CFA-65D05 [0A 0C 0A 0C 0A 0A 0A 0C 0A 0A 0A 0C] Music value to use for each boss battle(not the bank) (For x-4 boss music, use 0A here and level header setting 3 or 5; for x-8 boss music, use 0C here (or 0A for longer intro found in piranha/raven battles) and header setting 7 or 8.)

66769-6678C Boss Palette Pointers(After transformation)
[CA A5 5F] 1-4 Burt the Bashful
[22 21 70] 1-8 Salvo the Slime
[22 21 70] 2-4 Bigger Boo
[22 21 70] 2-8 Roger the Potted Ghost
[A2 21 70] 3-4 Prince Froggy
[22 21 70] 3-8 Naval Piranha
[06 A6 5F] 4-4 Marching Milde
[22 21 70] 4-8 Hookbill the Koopa
[82 21 70] 5-4 Sluggy the Unshaven
[8E A5 5F] 5-8 Raphael the Raven
[42 A6 5F] 6-4 Tap-Tap the Red Nose
[C2 21 70] 6-8 King Bowser

6678D-667B0 Boss Palette Pointers(Before transformation) (Warning: For some reason, changing the pre-transformed palette pointers for x-4 bosses will result in them using the wrong palette... however, if you leave the pointer unchanged, the boss will appear fine.)
[02 21 70] 1-4 Burt the Bashful
[22 21 70] 1-8 Salvo the Slime
[82 21 70] 2-4 Bigger Boo
[22 21 70] 2-8 Roger the Potted Ghost
[22 21 70] 3-4 Prince Froggy
[22 21 70] 3-8 Naval Piranha
[A2 21 70] 4-4 Marching Milde
[22 21 70] 4-8 Hookbill the Koopa
[82 21 70] 5-4 Sluggy the Unshaven
[42 21 70] 5-8 Raphael the Raven
[42 21 70] 6-4 Tap-Tap the Red Nose
[02 21 70] 6-8 King Bowser

Tip: ~~X-4 bosses should always be used in X-4 levels, and X-8 bosses should always be used in X-8 levels.~~ Actually, as Zeldara109 pointed out, bosses can be used in any level of a world. However, the settings only allow for one X-4 and one X-8 boss per world.

In addition, if using the Tap-Tap boss in a level other than 6-4, you'll need to change the values at 79E4D, 79ECF, 79FF2, and 7A20D [3F by default] to the translevel number (not level number) that you're using the Tap-Tap boss in... Otherwise, the transformation scene will be skipped. (However, if you do skip the scene, you may be able to use the Tap-Tap boss without the correct world-specific settings...)

Also, if you're using an x-4 boss at the end of a world or an x-8 boss in the middle of a world, you may also want to add/remove the key scene at the end of the battle. This can be done with hex-edits available here.

Then, it is highly recommended that you start with the exact room the boss originally appeared in (if you already overwrote that room, open it in a clean ROM and reconstruct it in your hack to the best of your ability).

Yoshi's entry position, the exact location of the boss sprite and other sprites, and various other things (especially header settings) may affect the boss battle. I strongly recommend making one change at a time, and testing the boss battle after each change-- even something as simple as editing the background color may result in unexpected glitchiness.
Why isn't (insert other sprite here) working?: It depends on the specific sprite. However, in general, it can help to check the levels in the original game that use that sprite (checking existing YI hack levels can also help), and compare the header settings and surrounding object layouts.
How do I make a pipe generate Shy Guys?: Simply place Sprite 01E (Shy Guy) on the top left tile of Object F4 (unenterable vertical pipe). This will only work if the entrance is at the top of the pipe; attempting this with an upside down pipe will not work.
Why do my Shy Guys appear in front of pipes?: Shy Guys will appear in front of Object 3C (enterable vertical pipe) instead of appearing behind it. If you wish to make a Shy Guy-generating pipe enterable, you instead have to use Object F4, and place Sprite 042 (vertical pipe entrance) on the top left corner of the pipe. This sprite will allow Yoshi to enter the pipe by pressing down.

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