Text (MI+errata): 12/12, Trample. ; When ~this~ enters the battlefield, sacrifice it unless you sacrifice any number of creatures with total power 12 or greater. [Oracle 2009/07/08]
It is sacrificed as a triggered ability. When it enters play put the ability on the stack. Players may respond to this before it resolves. When the ability resolves you choose whether to sacrifice it or 12 power in creatures. [D'Angelo 2007/07/15]
When it phases in, it is not "coming into play" due to the phasing rules. So you don't have to sacrifice again when it phases in. [D'Angelo 1999/07/29]
The sacrifices are simultaneous, not one at a time. So if have a Keldon Warlord and 6 other creatures, you have a 7/7 Warlord, and you can sacrifice it and 5 other creatures all at once to pay the cost. [D'Angelo 2000/02/25]
