InfectInfect is a static ability.
Damage dealt to a player by a source with infect doesn’t cause that player to lose life. Rather, it causes that source’s controller to give the player that many poison counters. See rule 120.3.
Damage dealt to a creature by a source with infect isn’t marked on that creature. Rather, it causes that source’s controller to put that many -1/-1 counters on that creature. See rule 120.3.
If an object is no longer in the zone it’s expected to be in as an effect causes it to deal damage, its last known information is used to determine whether it had infect.
The infect rules function no matter what zone an object with infect deals damage from.
Multiple instances of infect on the same object are redundant. (CR 702.90) (This creature deals damage to creatures in the form of -1/-1
countersTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) and to players in the form of
poison countersA player with ten or more poison counters loses the game. (CR 704.5c).)
When this creature
diesIs put into a graveyard from the battlefield. (CR 700.4),
proliferateTo proliferate means to choose any number of permanents and/or players that have a counter, then give each one additional counter of each kind that permanent or player already has.
In a Two-Headed Giant game, poison counters are shared by the team. If more than one player on a team is chosen this way, only one of those players can be given an additional poison counter. The player who proliferates chooses which player that is. See rule 810, “Two-Headed Giant Variant.” (CR 701.34). (Choose any number of permanents and/or players, then give each another
counterTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) of each kind already there.)