An interesting piece of info about Tail's Sky Patrol is that it didn't start as either a Game Gear or Tails game at all. In fact, the game was made by Japan System House/Biox as a launch game for what sounds like a cancelled handheld that was never announced, then ported to the GG to recoup development costs. Sega/SIMS's only involvement in terms of development was adding Tails and adding elements of Sonic's world, along with some rebalancing. This is a translation of
a Twitter thread by the original programmer that explains the whole story, found on
GDRI:
"There's this Game Gear game called Tails' Sky Patrol. I have quite a few memories of this game. Probably because I made it three times. Other than the Game Gear version, there were two other versions of the game completed.
The first version was for an unannounced game system (let's call it "X"). "X" had a monochrome LCD screen, Z80 CPU, one BG layer plus sprites, and the sound was two channels plus PCM. It was a very standard design, meant as a cheaper alternative to the Game Boy, aimed at a younger audience with an educational focus.
The X version was planned as a launch title. It's not often you get to work on a launch title, and it was also my first time working on an action game, so I put a lot of effort into it. I was responsible for all of the programming. It was a new platform, so there wasn't really any development environment, so I also built the tools. Near the end of production, we were short on resources so I asked someone else to do some of the boss programming.
The original X version didn't have Tails as the main character. I can't give any particulars, but the enemy designs still have the same impression as the original, so I'll let you use your imagination.
Even though the game was completed, before they could put out even a press release, the entire X project was cancelled, so only those involved in it even knew it existed. To recoup some of the costs of developing the game, we were asked if we could get the game running on the Game Gear, which had similar specs to the X. Because the CPU was the same and the resolution was very close, I thought I could get the game running as-is on the Game Gear, so I started out making a translation API for the Game Gear hardware, and built an emulator to translate the monochrome data to GG character data. I think it took about two weeks to get it running, but the graphics were still monochrome, which obviously wouldn't fly on the color Game Gear.
The business team went to Sega, who decided to put Tails in the game. At that point, proper development on the Game Gear version started. The game itself was the same, but there were some changes in the world design to fit the license, if I remember right. By this point, I was working on Ristar for the Game Gear, and a different team handled Tails. They redrew the character graphics, added demo scenes and a training stage, and adjusted the game balance for the Game Gear hardware. The X version was actually a 1M ROM, and it was quite an ordeal packing the map data into that space. The GG version was 4M, so they had a ton of space to add things. There was so much space that the character data didn't even need to be compressed.
It was of course released as Tails' Sky Patrol. It combines action, shooting, and racing elements, and has a unique game design that I don't think you'll find anywhere else.
About five years later, for reasons I can't say, we needed to produce a Game Boy title on an extremely tight schedule. We decided to do a port of Tails' Sky Patrol. Of course, Sega owned the rights to the characters so we had to redraw them, but our company owned the program. It's probably easier to think of it as a port of the X version.
Development was handled by staff from the same team as Daiku no Gensan, Kachikachi no Tonkachi ga Kachi, and Samurai Kid. Just like the port to the Game Gear, the characters were redrawn, demo scenes added, and the design was adjusted for the Game Boy. Porting the programing from the Z80 to the 8080 was quite difficult because the IX and IY registers couldn't be used. I was actually hospitalized during development, and I'm sorry for any additional pressure this put on the rest of the staff.
The game was completed as a GB/GBC dual compatible title. I'm hugely thankful for everyone on the staff for making a well-built title with a really cool character. The GB version was called "Boon Boon Kabun" and the completed version was shown off by Nintendo. Unfortunately, because of contract reasons, the release was cancelled even though the game was complete. In all my years working in the game industry, this and the X version were the only titles I've worked on that were cancelled after completion. Even today I still regret what happened.
That said, for me personally Tails' Sky Patrol was where I got my start with action games. If it weren't for that title, we wouldn't have had GG Ristar or Samurai Kid, either."
Another interesting line, other than the part about a full, unreleased Game Boy port without Tails existing, is this:
"The original X version didn't have Tails as the main character. I can't give any particulars, but the enemy designs still have the same impression as the original, so I'll let you use your imagination."
I wonder if this means that the original version was also based on an established license?