Skrolk, Disease-That-Walks

Overlord (must be a commander), Putrid (colorless mana is paid with Putrid mana), Infect, Lifelink, Greater Persist (2 -1/-1 counters before it disables), Incapacitation (Skrolk is tapped for 3 turns upon entering the command zone)

{x}Pox Prayer:Create X Plague cards.
{t}Putrescent Horde: Use X Putrid mana, then summon X tapped Plague Monks. For each mana spent, Skrolk loses 1 health.
{b}{b}{b}{t}Buboes: Opponent sacrifices a creature. Summon 2/1 Plague Rats equal to the toughnes