I have also notes that their are many overlaps when it comes down to a deity powers but when it comes down to Shar Selune and Mystra Shar is the goddess of darkness Selune is the goddess of the moon and Mystra is the goddess of the stars they do overlap a bit but they are not one in the same thing

Cthulhu: FOR THOUSANDS OF YEARS I LAY DORMANT, WHO HAS DISTURBED MY- Oh its you...
Warlock: Greetings my lord-
Cthulhu: LET ME SLEEP-