As a DM, I don’t think you should be using Power Word Kill at all. “I’ve set up this awesome encounter that you’re all going to love. Except you. You’ll have to sit this one out.”
Makes for a great BBEG move to use against a favorite DMPC or other beloved party companion, though. You don’t use it on a player, you use it on their feelings.
As a DM you should not be asking your players about their HP totals directly in order to target them with Power Words (or Sleep)
As a DM, I don’t think you should be using Power Word Kill at all. “I’ve set up this awesome encounter that you’re all going to love. Except you. You’ll have to sit this one out.”
Makes for a great BBEG move to use against a favorite DMPC or other beloved party companion, though. You don’t use it on a player, you use it on their feelings.