A poison counter is a counter that, unlike most other counters, is placed on players rather than objects. When a player has ten or more poison counters, that player loses the game. A player with at least one poison counter is considered poisoned.
Poison is intended to be a fundamentally different win condition from life totals because poison counters cannot be removed. Leeches, from Homelands, is the only exception to this rule. That exception is seen as a severe mistake, and the card would never be reprinted, even if it were not on the Reserved List. This is something the Mystery Booster test card Puresteel Angel teases.
However, a player may use Karn Liberated to restart the game and remove the poison counters in the process. Another way to counteract poison counters is to play Melira, Sylvok Outcast. While functionally unusable, Suncleanser also has the ability to remove poison counters, albeit only for your opponents.
The poison mechanic was introduced on the Legends cards Pit Scorpion and Serpent Generator. The mechanic appeared in sets up until Visions, and was planned as the main theme of Tempest, before it was retired from the game. It was next considered for Unglued 2 prior to that set's cancellation.
Poison appeared in a limited capacity in Future Sight, on a pair of futureshifted "preprint" cards with the keyword poisonous. It finally saw print as a major mechanic in Scars of Mirrodin block, which supported the poison counter-granting infect keyword with proliferate. The second set of that block, Mirrodin Besieged, expanded the concept by defining players as "poisoned" if they had one or more poison counters, and including cards that referenced that term.
Players with at least ten poison counters, and Two-Headed Giant teams with at least fifteen poison counters, immediately lose the game.
In the Comprehensive Rules
- Poison Counter
- A counter that may be given to a player. See rule 122, “Counters,” and rule 704.5c.
104.3d defines the how poison counter works:
- 104.3d If a player has ten or more poison counters, that player loses the game the next time a player would receive priority. (This is a state-based action. See rule 704.)
122.1d defines the term "poisoned":
- 122.1d If a player has ten or more poison counters, that player loses the game as a state-based action. See rule 704. A player is “poisoned” if they have one or more poison counters. (See rule 810 for additional rules for Two-Headed Giant games.)
704.5 and 704.6 define the various state-based actions, of which two relate to poison:
- 704.5c If a player has ten or more poison counters, that player loses the game. Ignore this rule in Two-Headed Giant games; see rule 704.6b instead.
- 704.6b In a Two-Headed Giant game, if a team has fifteen or more poison counters, that team loses the game. See rule 810, “Two-Headed Giant Variant.”
810.10 and 810.11 specify how poison works in Two-Headed Giant and with "further heads":
- 810.10. Effects that cause players to get poison counters happen to each player individually. The poison counters are shared by the team.
- 810.10a If an effect needs to know how many poison counters an individual player has, that effect uses the number of poison counters that player’s team has. If an effect needs to know how many poison counters a player’s opponents have, that effect uses the number of poison counters opposing teams have.
- 810.10b If an effect says that a player loses poison counters, that player’s team loses that many poison counters.
- 810.10c If an effect says that a player can’t get poison counters, no player on that player’s team can get poison counters.
- 810.10d If a rule or effect needs to know what kinds of counters an individual player has, that effect uses the kinds of counters that player has and the kinds of counters that player’s team has. A player is “poisoned” if that player’s team has one or more poison counters.
- 810.11. The Two-Headed Giant variant can also be played with equally sized teams of more than two players. For each player a team has beyond the second, that team’s starting life total is increased by 15 and the number of poison counters required for the team to lose is increased by five. (These variants are called Three-Headed Giant, Four-Headed Giant, and so on.)
Poison counters are granted by two keyword abilities.
Many older cards referencing poison counters use a wording very similar to the poisonous keyword, but trigger on any damage, rather than just combat damage. To avoid changing functionality, no errata were made for these cards when the poisonous keyword was introduced.
- Crypt Cobra
- Marsh Viper
- Pit Scorpion
- Sabertooth Cobra
- Serpent Generator
- Suq'Ata Assassin
- Swamp Mosquito
- Mark Rosewater (December 2, 2012). "What is it specifically...". Blogatog. Tumblr.
- Mark Rosewater (January 6, 2014). "You said that infect...". Blogatog. Tumblr.
- Mark Rosewater (November 22, 2012). "Just to nitpick...". Blogatog. Tumblr.
- Mark Rosewater (December 16, 2012). "do you get mixed feelings...". Blogatog. Tumblr.
- Monty Ashley (April 20, 2011). "The Changing Face of Poison". magicthegathering.com. Wizards of the Coast.
- Mark Rosewater (November 24, 2014). "Top 8 and a Half Tales". magicthegathering.com. Wizards of the Coast.
- Mark Rosewater (September 06 2010). "Something Wicked This Way Comes, Part 1". magicthegathering.com. Wizards of the Coast.
- Magic Arcana (June 27, 2005). "Mad Beetdown!". magicthegathering.com. Wizards of the Coast.
- Wizards of the Coast (January 10, 2011). "Mirrodin Besieged mechanics". magicthegathering.com. Wizards of the Coast.