An instant is a card you can cast at almost any time you have priority — during your turn, on an opponent's turn, in response to another spell, or before combat damage. Unlike permanents, an instant doesn't stay on the battlefield: after it resolves, its effect happens and the card goes to the graveyard. This timing flexibility makes instants the backbone of reactive play, letting you answer threats, protect your creatures, or disrupt an opponent's plans at the exact moment it matters.
In a deck, instants fill roles that demand speed and surprise: removal, countermagic, combat tricks, and card draw. Because they can be held up and used on an opponent's turn, they reward keeping mana open and reading the flow of the game. Many strategies rely on instants to stay interactive, and some decks are built entirely around chaining them together.
