Grotag Thrasher

• WWizards of the Coast2010-03-01
  Official Ruling
  The targeted creature is prohibited from blocking any creature this turn, not just Grotag Thrasher.
• WWizards of the Coast2010-03-01
  Official Ruling
  Grotag Thrasher’s ability can target any creature, not just one the defending player controls. For example, if you want that player’s creatures to be able to block this turn, you can target Grotag Thrasher with its own ability.

Rulings via Scryfall