Ambiguity is a rare Enchantment card from Unhinged (UNH), collector number 24. Current market price: $0.80 (foil $6.73), TCGplayer market prices via Scryfall.
Whenever a player plays a spell that counters a spell that has been played or a player plays a spell that comes into play with counters, that player may counter the next spell played or put an additional counter on a permanent that has already been played, but not countered.