When the MCD-212 'VDSC' is in two-region mode - which allows more explicit control over windowing/mixing effects - it shouldn't process the region control registers if the first region control register for each plane (indices 0 and 4, respectively) have an operation code of 0.
By continuing to process further region control registers, it can lead to the weights for a given plane being changed partway through the line, when the plane weights should be held where they were at the start of the line. This could inadvertently cause a fully-visible scanline to abruptly become invisible, but in the case of The Apprentice, it led to the planes being turned back on, which was causing 16 lines of flickering garbage at the bottom of the screen.
With that out of the way, The Apprentice looks much better.
I'm still in the process of blowing the dust out of the MCD-212 device at the moment, so I haven't submitted a pull request yet, but it will be interesting to see if this has a positive effect on any other games.
Edit: Also, I'm aware the game should have audio prior to going in-game. I intend to look into it once I've finished cleaning up the MCD-212/VDSC.
Incidentally, the VDSC is used in nearly all late-model CD-i players. However, earlier models based on the "Mini-MMC" board (which include the 605, and 910 players) used 2x VSC/VDC. The latter chips are what Magic Card are based off of. The former (VDSC) more or less rolls the functionality of the latter (VSC/VDC) chips into one package, hence the name.
