I've worked on fixing more graphics related bugs (one of which was very silly and prevented 64x64 tilemaps working). I'm sure they'll be more to uncover yet. I've implemented horizontal and vertical tile flipping.
Super Mario World now partially works. Obviously, there are no sprites yet, and graphics emulation is incomplete. It doesn't run any further than the second screen at the moment, due to some kind of CPU/Interrupt bug which affects a bunch of ROMs. I'll try to solve this soon.