Wall of Fungus

Defender, infect (This creature can't attack, and it
deals damage to creatures in the form of -1/-1 counters
and to players in the form of poison counters.)
At the beginning of each opponent's end step,
destroy all untapped creatures with a -1/-1
counter that didn't attack this turn.

"Be careful what you try to eat out here." -Bob's final
words of wisdom.