L3InitXX_InitSMWL3Clouds:

LDA #$17			;
STA $212C			; put all three layers on the main screen
STZ $212D			; and none of them on the subscreen
LDA #$04			;
TRB $40				; disable Layer 3 from being affected by CGADSUB

L3MainXX_SMWL3Clouds:

REP #$20				;
LDA $1E				; Layer 2 X position
LSR					; divided by 2
STA $22				; equals the X position for Layer 3
LDA $20				; Layer 2 Y position
CLC					;
ADC #$0050			; plus 50
STA $24				; equals the Y position for Layer 3
SEP #$20				;
RTL					;

LDA #$17
	STA $212C
	REP #$20	;Make A 16 bits wide
	LDA $1462		;Load the layer 1 x position
	LSR		;Divide by 2.  The more times you use LSR the slower the background will 

scroll horizontally.
	LSR		;If you use ASL (multiply by 2) instead the background will scroll 

faster than the foreground.
	STA $22		;Store to the layer 3 x position

	LDA $1464		;Load the layer 1 y position
	LSR		;Same as above, but vertically.
	LSR
	SEC		;These two lines are for shifting your background vertically.
	SBC #$0D20	;If you're using a background that loops you probably won't have to use 

this.
	STA $24		;Store to the layer 3 y position
	SEP #$20	;Make A 8 bits wide
	LDA #$17
	STA $212C

	LDA $0100		; game mode
	CMP #$11		; check if black screen (mario start where applicable)
	BNE NMI_GAMEMODE
	LDA #$78		; reset HDMA channels
	TRB $0D9F
NMI_GAMEMODE: