2014-05-29 : Use the powers of the creatures as they last existed on the battlefield to determine the value of X, even if they were negative. For example, if the sacrificed creatures were 3/3, 5/5, 0/4, and -2/2, the Demon will be 6/6.

2014-05-29 : You choose which creature you are sacrificing first, then each other player in turn order does the same. The creatures are all sacrificed simultaneously.