Repel Intruders

• WWizards of the Coast2008-05-01
  Official Ruling
  You choose whether or not to target a creature spell before you decide whether or not to spend on Repel Intruders. You may target a creature spell and then not spend to cast Repel Intruders; if you do, Repel Intruders simply won’t affect that creature spell. Similarly, if you don’t target a creature spell but then you spend to cast Repel Intruders, that part of Repel Intruders has no effect.
• WWizards of the Coast2008-05-01
  Official Ruling
  If you choose to target a creature spell, Repel Intruders has a target. If that target becomes illegal by the time Repel Intruders resolves, the entire spell won’t resolve. You won’t get any tokens.
• WWizards of the Coast2016-06-08
  Official Ruling
  If this spell is copied, the copy will not have had any colors of mana paid for it, no matter what colors were spent on the original spell.
• WWizards of the Coast2016-06-08
  Official Ruling
  This spell checks on resolution to see if any mana of the appropriate colors were spent to pay its cost. It doesn’t matter how much mana of that color was spent; the effect isn’t multiplied.
• WWizards of the Coast2016-06-08
  Official Ruling
  This spell cares about what mana was spent to pay its total cost, not just what mana was spent to pay the hybrid mana symbol in its cost.

Rulings via Scryfall