Enchantment, 1B (2) When a nonblack creature comes into play, sacrifice Grave Peril. If you do, destroy that creature. "Sometimes the grave does not wait for death before relishing its feast of flesh and bones."
—Ezrith, druid of the Dark Hours
Illus. Daarken
The sacrifice is not optional. [Future Sight FAQ 2007/05/01]
If more than one nonblack creature comes into play, this card will trigger for each of them. The first trigger that resolves will have you sacrifice this card and destroy that creature. The other triggers that resolve will be unable to sacrifice this card so they will not destroy any creature. [Future Sight FAQ 2007/05/01]
You choose the order the triggers go on the stack if they all happen at once so you can control which creature will be destroyed. [D'Angelo 2007/06/04]