> Hi Haze, I've just played MAME again and I'm sure you are now correct.
> I'm not entirely convinced that my PCB and the PCB on the video I sent yesterday are
> originals (although they look like it).
> So, the 'priority' may be something the copy boards missed out since this behavior is
> present on at least two different boards.
> When those winged aliens go underneath certain areas, you can bomb the background to
> reveal the winged alien fully. You can then dock with these winged aliens (by bombing
> them). Therefore, it is likely a gameplay feature that you need to destroy the
> background (in certain areas) to then be able to dock with the winged alien.
> Possibly worth putting a comment in the driver to mention this explicitly - ignore
> the behavior on copy boards.
> We need someone with a known original to absolutely confirm it but I'd say you are
Right. That was my feeling, the gameplay depends on it, and would be illogical with the sprite placement you're seeing on the PCB.
There's also Break Thru on the same hardware that might provide further test cases (unless there's an undumped priority PAL PROM and the broken boards are conversions?, although MAME uses the same priority system for both and nobody has reported Break Thru to be broken in MAME)