Horseless Headless Horsemann

Indestructible, Infect (This creature deals combat
damage to creatures in the form of -1/-1 counters and
to players in the form of poison counters.)
Horseless Headless Horsemann can't be blocked.
Horseless Headless Horsemann attacks each turn
if able.
Horseless Headless Horsemann can't attack
unless defending player is poisoned.