2013-07-01 : Shadowborn Apostle’s first ability lets you ignore only the “four-of” rule. It doesn’t let you ignore format legality.

2013-07-01 : You don’t have to sacrifice the Shadowborn Apostle whose ability you activated. It can be six other Shadowborn Apostles.

2013-07-01 : You sacrifice the six creatures when you activate the ability. You can’t respond to that ability by activating the ability of one of the other Shadowborn Apostles you just sacrificed.