Mystic Marsh
Land (Rare)

At the beginning of your end step, if you didn't cast any spells this turn, Mystic Marsh deals 1 damage to you.

Tap: Add U to your mana pool. If you played a land this turn, Add B to your mana pool instead.

B, Tap, Sacrifice Mystic Marsh: Target player gets a poison counter.

Steve Guay