Grave Peril

• WWizards of the Coast2007-05-01
  Official Ruling
  If multiple nonblack creatures enter at the same time, Grave Peril will destroy only one of them. Grave Peril's ability will trigger multiple times, but only the first one to resolve will do anything.
• WWizards of the Coast2007-05-01
  Official Ruling
  If a nonblack creature enters and Grave Peril triggers, then another nonblack creature enters, Grave Peril will trigger again and destroy only the last creature to enter.
• WWizards of the Coast2007-05-01
  Official Ruling
  This ability is not optional.

Rulings via Scryfall