The system features a revised motherboard that no longer includes the expansion port. This makes the Genesis 3 incompatible with the Mega-CD. The Genesis 3 launched at a recommended retail price of $49.95, which quickly fell to $19.99 due to a lack of interest in the system.
The console is also incompatible with the 32X and Power Base Converter due to additional revisions on the motherboard. Certain software is also made incompatible by these revisions. Virtua Racing is the main example, but games like Gargoyles are also incompatible due to a bug fix that was implemented in the console’s I/O controller. Gargoyles is specifically programmed to make use of the I/O controller bug, hence why it becomes incompatible with the Genesis 3.
-segadriven.com