A counter is a card or cards that can be used to offset or even fully negate the effects of another specific card or group of cards. Reaction cards like Moat are generally not considered counters, as their defensive effects tend to be rather broad and direct, though some Reactions can be considered counters if their effects are specific or subtle enough. Given the wide spectrum of what cards can do, there is no one trait that signifies a good counter. Counters typically either defend against an Attack or stop or slow an opponent's powerful strategy.
 Representative examples
- Minion vs Treasury - the Minion's Attack can discard Treasuries that had been stacked the previous turn
- Library vs Militia - Library draws more cards than usual after Militia forces you to discard the worst cards in your hand
- Lookout vs Sea Hag - Lookout immediately trashes the Curse Sea Hag puts on your deck