I have not used many gods of the forgotten realms in my games, that’s why my favorite deity is one of my own.
In my setting there is a god for death and the unknown. A three-headed dog named Cerberus guards the gates of heaven and hell. And his spectral death dogs bring the souls of the deceased to him. Once brought before him his three heads go into discussion and lay down justice.
I just like to put pieces of our own mythology and put them in my games, be it with a changed lore. In my game he appeared once and it was a very memorable moment.