Phyrexian Mite

Toxic is a static ability. It is written “toxic N,” where N is a number.

Some rules and effects refer to a creature’s “total toxic value.” A creature’s total toxic value is the sum of all N values of toxic abilities that creature has.

Combat damage dealt to a player by a creature with toxic causes that creature’s controller to give the player a number of poison counters equal to that creature’s total toxic value, in addition to the damage’s other results. See rule 120.3.