What it does
Infect changes how a creature deals damage. Instead of dealing normal damage, creatures with infect deal damage to players as poison counters and to creatures as -1/-1 counters. A player who accumulates 10 poison counters loses the game, regardless of their starting life total.
The most common misunderstanding: infect damage to players doesn't reduce life—it only adds poison counters. Likewise, -1/-1 counters from infect stay on creatures permanently and can kill them by reducing toughness to zero. Combat damage and noncombat damage (like burn spells with infect) both follow these rules. Note that wither only deals -1/-1 counters to creatures, while infect does both.
In Commander, poison is a parallel win condition that bypasses big life totals—10 poison is far less than 40 life. Watch for proliferate and Inkmoth Nexus-style combos that race to lethal poison fast.













