Kicker {B} (You may pay an additional {B} as you cast this spell.)
When Benalish Sleeper enters the battlefield, if it was kicked, each player sacrifices a creature.
As Benalish Sleeper’s ability resolves, first the player whose turn it is chooses a creature to sacrifice, then each other player in turn order does the same knowing the choices made before them. Then all those creatures are sacrificed simultaneously.
If you kicked it, you may sacrifice Benalish Sleeper itself as its ability resolves. If you control no other creatures, you’ll have to sacrifice Benalish Sleeper.