Byron, Thornvine Agent

{b}{b}:Put a vine counter on target creature you
don't control with power less than or equal to
Byron's toughness. That creature doesn't untap
during its controller's next untap step. Activate only
as a sorcery.

At the beginning of each upkeep, each creature
takes 1 damage for each vine counter it has.

When Byron leaves the battlefield, destroy all vine counters.