Guilt-Ridden Soldier

Guilt-Ridden Soldier enters the battlefield tapped.
Guilt-Ridden Soldier gets -1/-1 for each Human
or Soldier creature on any graveyard. If there is
no Human or Soldier creatures on any graveyard,
sacrifice Guilt-Ridden Soldier.
"I hear someone knocking at the south entry. Let's go
back to our bedroom. A little water will wash away
the evidence of our guilt. It's so simple! You've lost
your resolve. " -Lady Macbeth