Toxin Gorgo

Toxin (This creature deals damage to creatures in the
form of -1/-1 counters and to players in the form of
toxic counters. At the beginning of each player's
upkeep, that player puts the top X cards of their
library into their graveyard, where X is the number
of toxic counters they have.)
When Toxin Gorgo blocks put a poison counter
on target player unless that player pays {x},
where X is the number of toxic counters they
have.