Infect is keyword ability that started appearing on cards in Scars of Mirrodin. Flavor-wise, it is an ability of the Phyrexian side in the war over the plane of Mirrodin.
At first look it is a combination of abilities that have appeared in the past, poison and wither. Creatures with infect deal damage in the form of -1/-1 counters when damaging a creature or by giving poison counters when dealing damage to a player. The important thing to keep in mind is that prevention and redirection effects will still apply to this damage. For example, if the damage from an infect creature is prevented, no -1/-1 or poison counters will be given out.
Other abilities such as lifelink or deathtouch will still apply when an infect creature deals damage. For example, the card Flensermite from Mirrodin Beseiged has both lifelink and infect. When Flensermite deals damage, the creature or player receiving damage will receive the appropriate counter(s) and the controller of the Flensermite will gain life.
Finally, in two-headed giant games, it is important to note that a team does not lose to poison counters unless an individual player receives 10 or more poison counters. If one player on a team has one counter and the other has nine counters, that team is still in the game. When attacking in two-headed giant games you attack the opposing team. But anytime an attacking creature would deal damage to the team, either by being unblocked or via trample, the controller of the attacking creature must choose an individual player on the team to receive the damage. It is beneficial to have one player on the opposing team to get all of the poison counters as you only need to have that one player get 10 or more for the team to lose.
Today’s Rules Tip was submitted by Fabian Peck, a level 3 judge from Melbourne, Australia.