Siege Behemoth

• WOTC Official Reminder Textofficial rules
  Hexproof — This permanent can't be the target of spells or abilities your opponents control.

• WWizards of the Coast2014-11-07
  Official Ruling
  You decide whether to assign a creature’s combat damage as though it weren’t blocked just before it assigns that damage. You may make a different choice for each creature you control—that is, you may have none, some, or all of those creatures assign combat damage as though they weren’t blocked.

Rulings via Scryfall