Cannon

Each player chooses which card he or she will trash. The Coppers are gained into the player's hand, so if Cannon is played multiple times in a turn, players can trash the Coppers they have gained from a previous attack in response to a new attack.

Potion symbols are ignored, only he Coin values are counted.

A player's hand can exceed the normal size because of this. For example, if a player chose to trash Possession they would gain 6 Coppers into their hand.

Reactions which affect gaining cards such as Watchtower or Trader can be used in response to the gain.

Trashing a card with zero cost, such as a Copper or cards with costs reduced to zero by the Bridge wouldn't cause the gain of any cards.

If the Supply of Coppers runs out players still trash a card and gain nothing (or as many Coppers as they can if there are fewer than the cost of the card).