The other spell that you or a teammate cast can be one thatâ€™s resolved, one that was countered, or (for instants with surge) one thatâ€™s still on the stack.
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.
Grip of the Roil tracks the creature, but not its controller. If the creature changes controllers before its first controllerâ€™s next untap step has come around, then it wonâ€™t untap during its new controllerâ€™s next untap step.
Grip of the Roil can target a creature thatâ€™s already tapped. It still wonâ€™t untap during its controllerâ€™s next untap step.
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.
Casting a spell for its surge cost doesnâ€™t change its mana cost or its converted mana cost.