One approach I use in finding out that kind of information is the dma tracing ability. It's possible that the data could be being written to VRAM with manual writes, but it's far more common to see a DMA transfer as the final copying method. Assuming you're right and it's compressed graphics, it will be decompressed from the ROM into RAM at some location you don't know yet. But if you turn on DMA tracing right around the time you think the graphics end up in VRAM, it has enough info for you to figure out the RAM (WRAM) location where the transfer originated from. The real trick is getting to a point where the graphics are definitely not in VRAM yet. To do this you usually set up two savestates and view them in Vsnes. If you can verify that in the earlier savestate the graphics in question are not in VRAM, and they are in the later one, you simply can load the earlier savestate, turn on DMA tracing, and play until the point where the second savestate occurs. Then you sort through your the (probably large) list of DMA transfers to ascertain which one had the payload you're interested in.