Festering Wound 
Enchantment — Aura
Enchant creature At the beginning of your upkeep, you may put an infection counter on this Aura. At the beginning of the upkeep of enchanted creature's controller, this Aura deals X damage to that player, where X is the number of infection counters on this Aura.
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyLEGALvintageLEGALcommanderLEGAL