4 Oct 2004
Phasing in does not trigger "enters" abilities, so you don't have to sacrifice again if it phases in.
4 Oct 2004
The sacrifices are simultaneous, not one at a time.
15 Jul 2007
If the Dreadnought is no longer on the battlefield when the triggered ability resolves, you may still choose either option.
15 Jul 2007
Reverted to its original wording, this now has an "enters" triggered ability. During resolution of the triggered ability, you choose one option or the other.
15 Apr 2013
If you are unable to sacrifice 12 power worth of creatures, then you cannot choose that option; in that case, you must sacrifice Phyrexian Dreadnought.