This has puzzled me for a long time and it still does. While recently playing S3&K, I got to FBZ2 and saw the earthquake in that zone, when it occured to me to try using Gens' layer disabling functions. After disabling plane A I noticed that there was now a black bar where the floor should have been, and thought "hey, maybe it's just changing the position and base address of plane A on hblank?". This was possible for FBZ, but upon applying this thought to MGZ I am thoroughly confused. Here's some screenshots. All layers enabled in a part of the earthquake sequence. In the right picture, only sprites are disabled, to prove that the game doesn't just cheat by putting land on sprites. The game was paused via Start rather than emulator pause, hence the emulator timer changing. Plane A (left) and Plane B (right) disabled in the same area. Now, here's my thoughts at this time: 1. Since they put part of the layer Sonic's on (I shall call this layer 0 from now on, and the other layer 1) on plane B, why didn't they put it /all/ on plane B? If I had programmed the effect I would have thought this would be the only way to do it. 2. The only way this effect could be done in this way, that I can see, is that they used block vertical scrolling and changed the values on HBlank. However, 2 is wrong. Why? Because, after unpausing, letting the game run for a little longer and pausing again, we arrive at the next four screenshots (in the same order): Now, look at the screenshots above. As you can see, both layer 0 and 1 have remained on plane A, and the non-solid grass tiles are still on plane B. But notice that there are now tiles of both layers overlapping! You can see this in two places: the ceiling under the spikes, and the grass to the left of Sonic. While it is certainly possible for clever use of HBlanks and block vertical scrolling to allow these effects for rectangular areas such as in FBZ, this technique cannot possibly work for MGZ as any given 16x1 rectangle of the screen cannot possibly contain data from two 8x8 tiles on the same plane in the same frame. So, how is this possible? Right now I am thinking that the only way to do it would be to blit at least the overlapping tiles in software, but this seems like way too much programming effort not to mention the possible lag it may produce. As I mentioned before, I would have implemented the cutscene by placing layer 0 on plane A and layer 1 on plane B, which is exactly what Sky Sanctuary Zone does (with the clouds in the background on sprites). Anyone have any ideas about this?