Hinterland Scourge must be blocked if able. At the beginning of each upkeep, if a player cast two or more spells last turn, transform Hinterland Scourge.
. . . but the monster within was a tireless hunter.
2011-01-22
If Hinterland Scourge is attacking, the defending player must assign at least one blocker to it during the declare blockers step if that player controls any creatures that could block it.
2016-07-13
For more information on double-faced cards, see the Shadows over Innistrad mechanics article (http://magic.wizards.com/en/articles/archive/feature/shadows-over-innistrad-mechanics).