Falling wall is on-screen flag. Because the game puts two walls five spaces apart (one for the left and another for the right side), this one prevents the game to have two walls being occupied in the same spot. In addition, they use HDMA to draw their graphics and so two seperate walls can't co-exists at the same time due to this reason.
Flag to upload graphics from the Super FX buffer. Is the value positive then 0x2000 bytes are uploaded from $705800 into $5400 (i.e. the last four rows of the sprite graphics). Is the value negative then the VRAM destination is whatever is stored in $0CF9 & 0x7FE0 and the graphics come from $706800 instead. Upload size stays the same.