Gallows at Willow Hill

• WWizards of the Coast2012-05-01
  Official Ruling
  If the targeted creature is an illegal target when the ability tries to resolve, the ability won’t resolve and none of its effects will happen. The creature’s controller won’t put a Spirit token onto the battlefield.
• WWizards of the Coast2012-05-01
  Official Ruling
  You can tap any three untapped Humans you control, including ones you haven’t controlled continuously since the beginning of your most recent turn, to pay the cost of the activated ability.

Rulings via Scryfall