At the beginning of your upkeep, sacrifice a creature other than Lord of the Pit. If you can't, Lord of the Pit deals 7 damage to you.
11/17/2017 If you control any other creatures as Lord of the Pit’s triggered ability resolves, you must sacrifice one. You can’t choose to be dealt 7 damage instead.
11/17/2017 If Lord of the Pit has gained lifelink, being dealt 7 damage by it doesn’t cause your life total to change, even though you gain and lose life. If your life total is less than 7, you won’t lose the game.
11/17/2017 If you have two Lords of the Pit, you can sacrifice them to each other.