When Trench Gorger enters the battlefield, you may search your library for any number of land cards, exile them, then shuffle your library. If you do, Trench Gorger has base power and base toughness each equal to the number of cards exiled this way.
9/22/2011 If you choose not to search, Trench Gorger will simply be 6/6.
9/22/2011 While Trench Gorger’s ability is on the stack, it’s on the battlefield as a 6/6.
9/22/2011 If Trench Gorger leaves the battlefield before its triggered ability resolves, you may still search your library.
9/22/2011 After the ability resolves, Trench Gorger’s power and toughness won’t change if one of the exiled cards leaves exile.