Several Attack cards reduce the handsize of opponents by making them discard cards from their hand or return them to the deck—forcing them to start their next turn with fewer than the ordinary 5 cards, and thus reducing the amount they can accomplish on that turn.
Such Attacks are often well defended against by cards that redraw your hand up to a specified size (e.g. Library, Watchtower, Jack of all Trades), and by cards that are more likely to achieve their best effects if played in a small hand (Menagerie, occasionally Shanty Town). Decks built on cards that reduce their owners' handsize when played, such as Warehouse or Hamlet, are especially vulnerable to these Attacks.
A powerful combo involves playing a handsize attack and then Masquerade—forcing the victims to either discard their bad cards to the attack and pass a good card to the Masquerade, or to potentially discard good cards in order to keep a bad card in hand to pass. This is one of the key techniques underlying the notorious Masquerade Pin.
List of handsize attacks
Discard to target handsize
These attacks reduce the victim's handsize to a specific number of cards—usually 3—regardless of how many they had to begin with. This means that additional plays of the Attack after the first don't hurt opponents; they are already down to the target handsize. These can be especially useful to counteract the effects of cards that increase opponents' handsize, like Council Room and Governor, since a single play of the Attack will reduce the victims' handsize almost as effectively as if the handsize increaser had never been played.
- Dominion: Militia
- Intrigue: Minion
- Seaside: Ghost Ship
- Prosperity: Goons
- Cornucopia: Followers
- Hinterlands: Margrave
- Dark Ages: Sir Michael, Urchin and Mercenary
Stackable handsize attacks
These attacks can be repeated and continue to reduce players' handsize after the first play. These attacks either target specific cards, and will not continue reducing handsize if a player has none of the targeted cards in hand, or they can be prevented from reducing handsize if a player chooses to gain a Curse, or both.
- Dominion: Bureaucrat targets Victory cards
- Intrigue: Torturer allows a player to gain a Curse instead of discarding
- Seaside: Cutpurse targets Copper
- Prosperity: Mountebank is not generally considered a handsize attack; it can cause a player to discard a Curse, but this is regarded as a defense against Mountebank's cursing attack rather than a discard attack per se.
Pillage, from Dark Ages, targets a specific card in hand to discard (of the attacker's choice), rather than discarding to a target handsize, but it will not affect players with fewer than 5 cards in hand.