Poison counters are an alternate way of winning the game (see "Winning and losing"): when a player has ten (10) or more of them, that player loses the game. In Two-Headed Giant, a team with fifteen (15) poison counters loses the game. The poison mechanic was introduced in Legends but has never been strongly supported until the mechanic resurfaced in Future Sight and afterwards become a major theme in the entire Scars of Mirrodin block.
Since the counters have no other properties, and rarely any other card affects or is affected by them, they do not hold much power in the metagame. Two keyword abilites use poison counters to inflict damage: "Infect", and "Poisonous". With infect; how many poison counters a creature deals to an opponent is equal to its power: 1/1 = deals 1 poison counter. 3/2 = deals 3 poison counters. These are dealt instead of regular damage, not in addition to it. However, with "Poisonous", the number of poison counters dealt in damage is eaqual to the N value in Poisonous N. For example, a 1/1 creature with Poisonous 2 deals 2 poison counters, as well as the 1 (non-poison) Damage, from the creature's power.
Cards using poison counter(s) before the keyword Infect & Poisonous
- Crypt Cobra
- Marsh Viper
- Pit Scorpion
- Sabertooth Cobra
- Serpent Generator which creates Snake artifact creatures
- Suq'Ata Assassin
- Swamp Mosquito