Grip of the Roil

• WWizards of the Coast2016-01-22
  Official Ruling
  Casting a spell for its surge cost doesn't change its mana cost or its mana value.
• WWizards of the Coast2016-01-22
  Official Ruling
  The other spell that you or a teammate cast can be one that's resolved, one that was countered, or (for instants with surge) one that's still on the stack.
• WWizards of the Coast2016-01-22
  Official Ruling
  For some cards, surge represents only an alternative cost, a discount that applies if you or a teammate has cast another spell this turn. Other cards, like Reckless Bushwhacker, have additional abilities or effects if you paid the surge cost to cast the spell.
• WWizards of the Coast2016-01-22
  Official Ruling
  Grip of the Roil tracks the creature, but not its controller. If the creature changes controllers before its first controller's next untap step has come around, then it won't untap during its new controller's next untap step.
• WWizards of the Coast2016-01-22
  Official Ruling
  If an instant or sorcery spell cast for its surge cost is copied, the copy is also considered to have had its surge cost paid.
• WWizards of the Coast2016-01-22
  Official Ruling
  Grip of the Roil can target a creature that's already tapped. It still won't untap during its controller's next untap step.

Rulings via Scryfall