A question about the rules on Shadowborn Demon:
When Shadowborn Demon enters the battlefield, destroy target non-Demon creature.
At the beginning of your upkeep, if there are fewer than six creature cards in your graveyard, sacrifice a creature.
Firstly, I understand that you have to destroy a creature (even if it's your own), what if there are no other non-demon creatures out? Can you play the card?
If Shadowborn Demon is the only card on your side and you don't have six or more creatures in your graveyard do you have to sacrifice it?