There has been a long-standing known bug in dec0.c for some time (checking my notes, it's been there for 7 years!), in that row & column scroll could not be applied to a tilemap simultaneously. The reason for this limitation is that Mame's tilemap system did not support this. Anyway... I've re-implemented the rendering of this sytem by providing a new tilemap draw function that correctly implements simultaneous row & column scroll. I also verified the rendering of all video modes using a trojan on a Birdie Try board. This finally fixes the waterfalls in Midnight Resistance! (It doesn't really affect any other games, but the source code is much cleaner now).