This hack remove the gradient. There are two patches, one that removes it permanently, one that adds a menu option to toggle the gradient. Code could maybe be optimized (HDMA data and gradient table for no gradient option), but for now it is what it is.

For the free space used, $C0F091 code can be relocated elsewhere in same bank and $EFFBC8 code elsewhere in the ROM. I included some custom menu background screenshots examples with no gradient but these are not included with the hack.

no_gradient can be assembled with bass and menu_gradient with xkas (yeah, weird and this will change in future release if one).

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