You're welcome. No worries. There are instances when I'm not as free either, but I do try my best to make myself available.
Yes, you're correct. The Koopa Kids are determined by which world you're currently in, much like these other pipe systems. However, unfortunately, I've never bothered to try to seek out how the game controls them and their specific abilities by world yet, so I don't have any data to provide on that as of right now, but I do recall seeing the graphics for the Koopa Kids in Tile Layer Pro before, within the range of 0x52010 - 0x5300F. Depending on the current world selected, the game somehow determines which tiles to use from these graphics banks. I could maybe look into this further later on, if necessary.
The graphics bank is loaded into $071D in RAM, between #$48, #$49, and #$4A. The last quarter, #$4B, is used for when the Koopa Kid is spinning from a hit or defeat.
----------------------Koopa Kids by World (Write to $071D graphics bank).
$AEC4:AC 27 07 LDY $0727 = #$00
$AEC7:B9 72 AE LDA $AE72,Y @ $AE72 = #$48
$AECA:8D 1D 07 STA $071D = #$12
$AECD:B9 79 AE LDA $AE79,Y @ $AE79 = #$37
$AED0:8D 1E 07 STA $071E = #$4F
$AED3:AD BD 07 LDA $07BD = #$00
$AED6:20 99 FE JSR $FE99
0x2E82 ($AE72) - 0x2E88 ($AE78) (0x7)
48 49 4A 48 49 48 4A
0x2E82 - World 1: 48
0x2E83 - World 2: 49
0x2E84 - World 3: 4A
0x2E85 - World 4: 48
0x2E86 - World 5: 49
0x2E87 - World 6: 48
0x2E88 - World 7: 4A
Do you think that your project might require you to swap the order that the Koopa Kids appear?
Insectduel recently completed a hack that adds an 8th Koopa Kid, available in the General SMB3 Hacking Thread as well, as seen here
. Perhaps he has additional information that can be useful.
With regards to the airship sprite after it flies away from the castle, again, you're correct that there are other pointers used to determine which level to load, with a different level for each world.
----------------------Ship levels by World after the ship leaves the End Castle.
0x19291 - World 1 Objects: B7 AD (0x2EDC7)
0x19293 - World 2 Objects: AB AE (0x2EEBB)
0x19295 - World 3 Objects: 09 B0 (0x2F019)
0x19297 - World 4 Objects: 3A B1 (0x2F14A)
0x19299 - World 5 Objects: 97 AC (0x2ECA7)
0x1929B - World 6 Objects: B3 B2 (0x2F2C3)
0x1929D - World 7 Objects: 89 B4 (0x2F499)
0x1929F - World 8 Objects: 17 B6 (0x2F627) (Crappy Ship)
0x192A1 - World 1 Enemies: EA D6 (0xD6FA)
0x192A3 - World 2 Enemies: 1C D7 (0xD72C)
0x192A5 - World 3 Enemies: 57 D7 (0xD767)
0x192A7 - World 4 Enemies: 98 D7 (0xD7A8)
0x192A9 - World 5 Enemies: A6 D6 (0xD6B6)
0x192AB - World 6 Enemies: E5 D7 (0xD7F5)
0x192AD - World 7 Enemies: 14 D8 (0xD824)
0x192AF - World 8 Enemies: 67 D8 (0xD877) (Crappy Ship)
Similarly, the Coin Ship can be different for each world as well if the hacker so chooses, though in the original game, the same level is used for each world.
----------------------Coin Ships by World.
0x19337 - World 1 Objects: 15 BC (0x2FC25)
0x19339 - World 2 Objects: 15 BC (0x2FC25)
0x1933B - World 3 Objects: 15 BC (0x2FC25)
0x1933D - World 4 Objects: 15 BC (0x2FC25)
0x1933F - World 5 Objects: 15 BC (0x2FC25)
0x19341 - World 6 Objects: 15 BC (0x2FC25)
0x19343 - World 7 Objects: 15 BC (0x2FC25)
0x19345 - World 8 Objects: 15 BC (0x2FC25)
0x19347 - World 1 Enemies: 04 DA (0xDA14)
0x19349 - World 2 Enemies: 04 DA (0xDA14)
0x1934B - World 3 Enemies: 04 DA (0xDA14)
0x1934D - World 4 Enemies: 04 DA (0xDA14)
0x1934F - World 5 Enemies: 04 DA (0xDA14)
0x19351 - World 6 Enemies: 04 DA (0xDA14)
0x19353 - World 7 Enemies: 04 DA (0xDA14)
0x19355 - World 8 Enemies: 04 DA (0xDA14)
You might wonder, can a Coin Ship really appear in any world? In the original game, it would only appear in Worlds 1, 3, 5, and 6. Well, that's because there were only Hammer Brothers (Sprite #$03) in those worlds. In World 2, there were Boomerang and Fire Brothers; in World 4, there were Sledgehammer Brothers; and in World 7, there were Plants.
So, if the hacker includes a Hammer Brother in each world, there is the potential to access the Coin Ship in those worlds, possibly with the exception of World 8, much like how the N-Spade Bonus Game won't appear there, but I haven't actually bothered to test that out yet. Just throwing that out there.
The code that looks for a Hammer Brother (Sprite #$03) after clearing a stage with a coin total equal to a multiple of 11, and the tens digit of the player's score matching the multiple of 11, is located at 0x16D55 ($AD45) in the ROM.
$AD45:B9 15 7F LDA $7F15,Y @ $7F17 = #$03
$AD48:C9 03 CMP #$03
$AD4A:F0 06 BEQ $AD52
$AD4D:C0 0E CPY #$0E
$AD4F:D0 F4 BNE $AD45
$AD52:A9 0B LDA #$0B
$AD54:99 15 7F STA $7F15,Y @ $7F17 = #$03
Specifically, if the game finds a #$03, it will replace it with #$0B, the White Coin Ship (Takara! Kawaii).
This turned out to be a lot for one post, so sorry if it's too much. SMB3 is definitely my favourite game, and I enjoy seeing others working on SMB3-related projects!
If you wish, please feel free to PM or email me if you ever have any other questions about anything. I might not always have the full answer off-hand, but I can always try my best to help find something that might point you in the right direction. Just in case I might not always be able to get on here, either.
I wish you the best of luck with your project, and hope that your motivation stays strong to help you see it through to completion!