Traveling Plague 
Enchantment — Aura
Enchant creature At the beginning of each upkeep, put a plague counter on this Aura. Enchanted creature gets -1/-1 for each plague counter on this Aura. When enchanted creature leaves the battlefield, that creature's controller returns this Aura from its owner's graveyard to the battlefield.
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyLEGALvintageLEGALcommanderLEGAL