@_marco_1969 maybe u missing some thing.
Explain what u trying to archive, and what have u tried.
Actually you dont need a mask if u going for moon_type just create 8 images for the different moon types. Then use moon_type condition tag to make the one off the moon image appear and hide the rest
E.g moon_type = 1 on the calendar
The formule for image 1
([moon_type] == 1)?0:-100
Formula for image 2 is
[moon_type] == 2)?0:-100
And so on
If using moon_po then u got to follow the tutorial
If you did a search there is also a similar topic.