You don't actually need to pause the game to make it work, as the video demonstrates, it just makes it easier to do.

Done. xitter.cf/SCDDeconstruct/status/…

There's some bugs with the peelout in Sonic CD. There's certainly shenanigans to be had. (This does not apply to the remake, as that implemented it differently)

Thanks for the reminder. Looking into this.

The 2013 remake of Sonic 2 directly ported the Death Egg Robot from the original game, but broke the way its arms launched at Sonic.

Unreferenced demo data exists for special stage 2 in the v0.51 prototype of Sonic CD. It never gets decompressed into the demo data buffer nor does the code to run it get called. However, with some hacking, it can be restored.