I couldn’t confirm this information on any magazine articles from the era, so I can’t say if this is true story.
In 1991 Sega decided to jump into the online gaming, not like today with multiplayer online games, (this is a CD-i revolution with Ram Raid) no, just to download exclusive games.
To be able to do such a thing you needed some quite specific things.
– 1st, you needed to live in Japan or Brazil.
– 2nd, you needed a Sega Mega Drive.
– 3rd, you needed a Mega Modem add-on.
– 4th, you needed a Meganet subscription.
– 5th, you needed a game called Toshokan (or Sega Game Library).
This is where Sonic Eraser was available to download.
Well, nothing really special… very easy…
So what does it have to see with CD-i?
I found over the net some sites who claims that a Game Gear and a CD-i version was planed (as I said, I still can’t find any proof of that).
This is game developed by Sega, up to 2 players like Columns or Puyo Puyo.
The game was only available for a very limited world zone, so unknown for almost everybody until February 2004 when Sonic KulT website managed to get the Rom.
It will be hard to confirm the possible CD-i project due to the specificity of the game (Japan/Brazil zone & Online).
To be true, this means CD-i could also get a game from Sega Mascot, Sonic! Just like Philips did with Zelda’s and Mario!
You can try the game using the online emulator from Let’s Play Sega!