2019-01-25 : Because it may have targets, the ability of Priest of Forgotten Gods isn’t a mana ability. It uses the stack and can be responded to, even if no targets were chosen.

2019-01-25 : You can activate the ability of Priest of Forgotten Gods without choosing any targets if you wish. You’ll still add {B}{B} and draw a card.

2019-01-25 : You may target players who can’t sacrifice a creature. Those players still lose 2 life.