Hoser

A hoser can be something that destroys, prohibits, or prevents something specific. “Color hosers” are cards that punish players for playing a particular color. For example, the card Red Elemental Blast would be considered a "blue hoser", answering any blue card. On the other hand, the card Root Cage would be considered a "mercenary hoser", successfully dealing with mercenary creatures. Some such cards are "deck hosers", which serve to answer a specific match up or strategy that is expected to be prevalent in the metagame. Good examples of this are Trickbind or Stifle (against Storm combo) and Leyline Of The Void against Dredge. Hosers are often cheap; many of them cost 2 mana or less.

Hosers are best put in a sideboard to allow a deck to better deal with certain situations that the main deck is weak against. They exist on a sliding scale of power and versatility. The most powerful hosers such as Leyline of the Void which can almost guarantee winning a game are only that powerful against one deck or even one critical card but are near useless in a different matchup. Less powerful hosers such as Circle of Protection: Red can be brought in against a wider variety of decks but do not dominate the game to the same degree.

Enemy-colored hosing

 * Mask of Law and Grace (White enchantment that gives protection from black and red)
 * Flashfreeze</c> (Blue instant that counters a red or green spell)
 * Deathmark</c> (Black sorcery that destroys white or green creatures)
 * Ignite Disorder</c> (Red instant that deals damage to white or blue creatures)
 * Witchstalker</c> (Green creature that gets a +1/+1 counter when blue or black spells are cast)

Expansion hosing

 * Apocalypse Chime hosed cards from Homelands. It was the last "expansion hosing" card to be printed.
 * City in a Bottle hosed cards from Arabian Nights.
 * Golgothian Sylex hosed cards from Antiquities.