The classic side-scrolling shooter Gate of Thunder, packed along with the first two Bonk games was a special free treat for Duo buyers. Also hidden on the disc is a version of Bomberman. Pack-in title that came with the Turbo Duo console. Super CD-ROM2 format. Did not come in a case, it was packaged with just a slipcover and manuals.
Couple of things here that should probably be changed.

"a version of Bomberman" is the original TG-16 Bomberman HuCard.

"Did not come in a case, it was packaged with just a slipcover and manuals." Huh? I got my Duo the day they hit stores and my GoT/BA/BR disc was in a jewel case identical to the Y's I & II case (ie white tray, no insert). Every Duo I've come across had the same setup and I've never seen a slipcase for the disc. It could have been changed at some point I guess.

-Mike