Oracle Text

Gravecrawler can't block.

You may cast Gravecrawler from your graveyard as long as you control a Zombie.

Card Rulings

1/22/2011 Gravecrawler’s ability doesn’t change when you could cast it.
1/22/2011 Once you’ve cast Gravecrawler and it’s on the stack, it doesn’t matter if you lose control of the other Zombie.