Infect is a keyword ability.
What is infect?Creatures with infect deal damage to players and creatures in different ways than other creatures.
This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.
You've probably heard of +1/+1 counters. Creatures like Feral Hydra can put +1/+1 counters on themselves. An creature with Infect deals damage to creatures in -1/-1 counters instead of just dealing normal damage. Suppose an 2/2 Creature with Infect like Contagious Nim attacks. If the other player blocks with a 3/3, then instead of nothing happening when Contagious Nim deals its damage, it puts two -1/-1 counters on the 3/3 creature instead of dealing 2 damage. Now, the 3/3 creature is only a 1/1 creature. From then on, the creature weaker permanently unless they get +1/+1 counters again, negating its effects. Another part of Infect is that it deals poison counters to players. Normally, if a 2/2 creature attacks, and the opposing player lets the damage go through, that player would simply lose 2 life. But with infect, the player would get 2 poison counters instead. Here's the important thing: a player with 10 or more Poison counters loses the game.
There's only one way to get rid of poison counters: Leeches.
- 702.89a Infect is a static ability.
- 702.89b Damage dealt to a player by a source with infect doesn’t cause that player to lose life. Rather, it causes the player to get that many poison counters. See rule 119.3.
- 702.89c Damage dealt to a creature by a source with infect isn’t marked on that creature. Rather, it causes that many -1/-1 counters to be put on that creature. See rule 119.3.
- 702.89d If a permanent leaves the battlefield before an effect causes it to deal damage, its last known information is used to determine whether it had infect.
- 702.89e The infect rules function no matter what zone an object with infect deals damage from.
- 702.89f Multiple instances of infect on the same object are redundant.