It's okay if any of them are already tapped, and it's okay if any of them are controlled by someone other than the defending player
Like most Magic: The Gathering cards, the value of Stronghold Gambit depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Nemesis)
That creature deals damage equal to its power to up to one target creature you don't control
Assassin Gauntlet This is the cheapest card we have that generates this effect
Total Price : About $35-$40 (Look for a deal in person) and available in most big box hardware stores
It doesnt tell you specifically to fling this card at your opponent, but if youre sat across the table from someone while you battle, as is usual for card games, theyre right in the firing line