every time you insert a new layer and move it to up-down
all layers will automatically assigned a number
from bottom to top 0,1,2,3,4
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i know your problem is
in your game their might some special actions like
something on layer 1 or 2 or 3 or 4
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best way is always give them names to layer
0= BG
1=main
2=HUD etc
you can create any new layer and insert it
it will not effect to your conditions or action