Toxic is a new keyword ability which puts poison counters on a player when a creature with toxic deals combat damage to that player. Toxic is always followed by a number, called the toxic value. The toxic value tells you how many counters are given to that player. Unlike infect, which caused a creature to deal damage to players in the form of poison counters, toxic causes an additional effect.

Corrupted is an ability word which indicates abilities that care whether an opponent has three or more poison counters.

To proliferate, choose any number of players or permanents that have one or more counters on them. This can be any kind of counters: +1/+1 counters on creatures, loyalty counters on planeswalkers, even unusual things like time, charge, or doom counters.