db $42
JMP MarioBelow : JMP Return : JMP Return
JMP Return : JMP Return
JMP Return : JMP Return
JMP Return : JMP Return : JMP Return

MarioBelow:
    LDA $7D     ;\ Make sure to check whether Mario is actually hitting the block!
    BPL Return  ;/
    LDA $85     ;\
    EOR #$01    ;| Invert the water level flag.
    STA $85     ;/
Return:
    RTL

print "When hit from below, toggles whether the level is a water level or not."