Oracle Text

At the beginning of your upkeep, sacrifice Gurzigost unless you put two cards from your graveyard on the bottom of your library.

GG, Discard a card: You may have Gurzigost assign its combat damage this turn as though it weren't blocked.

Card Rulings

4/1/2008 You decide how it will assign its damage at the time the ability resolves. This will be prior to actually assigning combat damage.
4/1/2008 If this creature is attacking a planeswalker, assigning its damage as though it weren’t blocked means the damage is assigned to the planeswalker, not to the defending player.