Azkaban Prison

{t}{b}{b}
{t}Create a dementor token.
{t} Dementors Kiss: If you have more dementors
on the battlefield than an opponent has creatures,
exile one of their creatures (without Patronus)
under Azkaban Prison. If Azkaban Prison leaves
the battlefield, the exiled creature returns to it's controllers battlefield with -3/-3
They don't need walls and water to keep the
prisoners in...Most of them go mad within weeks...