The lost helper item

While on the subject of weird animations, I figured I should talk about this. Apart from the character-specific animations, Sonic has an unused animation in slot $A, which has the following definition:

byte_12BA8:     dc.b    9, $BA, $C5, $C6, $C6, $C6, $C6, $C6, $C6, $C7, $C7, $C7, $C7, $C7, $C7,
                dc.b  $C7, $C7, $C7, $C7, $C7, $C7, $FD,   0

What's interesting is that, beyond the regular standing sprite at mapping frame $BA, the animation is comprised entirely of otherwise unused sprites! Sonic is really the only character with unused graphics like that. This is what the animation looks like, which shouldn't surprise most of you lot:

Here we can see Sonic whistling. Calling someone, perhaps? Anyway, back when these sprites were first discovered, a few observant individuals made a connection between them and a certain debug element in standalone Sonic 3.

In Sonic 3, when using an S monitor, a whistling sound will be heard instead of the regular Super transformation sound:

What is the significance of this? Well, back in February 1994, German magazine Sega Magazin published their hands-on impressions of the game then known as Sonic 3 Part One. Specifically, in page 97 they describe the new power-ups in the game, providing descriptions of the three elemental barriers as well as a fourth item not found in the final game:

Water shield: Sonic can now breathe under water, and he also can use the Squat-Attack.
Fire shield: Is very effective against fire attacks. Sonic can use the Flying Attack with it.
Lightning-Shield: Sonic can electrocute near enemies.
Help!-Item: Tails helps him in dangerous situations.

Translation: Oerg866 (emphasis added)

And so a theory was born: originally, the S monitor wasn't a debug-only item that granted Sonic his super form, it was a helper item that triggered the whistling animation, which would summon a flying Tails to carry Sonic out of a jam. That's why the S monitor plays the whistling sound in Sonic 3: it's a leftover from the helper item the developers forgot to fix.

This is a reasonable hypothesis. It would certainly explain how precious VRAM got wasted on a monitor icon which can never be seen outside of debug mode.

I think that last point might be a red herring, though. The whistling sound also shows up in Sonic & Knuckles, where it's used in The Doomsday Zone. It is equally likely that the developers originally repurposed the whistling sound for Super transformations, but later changed their minds and forgot to update the S monitor. At least until Sonic & Knuckles.

Rather, looking at the order of the sounds in the Sound Test tells a different story:

ID	Description
$3E	Flame Barrier item box
$3F	Aqua Barrier item box
$40	(unused)
$41	Thunder Barrier item box
$42	Double Spin Attack
$43	Flame Barrier Attack
$44	Aqua Barrier Attack
$45	Thunder Barrier Attack
$46	Whistle

Note how the whistling sound appears directly after the sounds used for Sonic's elemental barrier attacks, which in turn are ordered the same as their respective item box sounds. Except for the unused sound effect in slot $40, that is, which actually sounds considerably more "electric" than the strange "ding" used by the Thunder Barrier item box.

My guess is that sound effect $40 was originally meant for the Thunder Barrier item box, whereas sound effect $41 was meant for the helper item's item box. The whistling sound (and matching animation) would only play later, once the item was actually used. Whether that was automated like the Super monitor, or something that could be stored for later, we'll probably never know.

I should point that Sonic Generations uses sound $40 for the Thunder Barrier item box, but whether that was by design or due to lack of attention to the source material is up for grabs.