MTG Combo: Grave Pact + Kalitas, Traitor of Ghet + Virulent Plague
When an opponents creature dies, Kalitas creates a 2/2 zombie token. Virulent Plague instantly kills the token, triggering Grave Pact. When your opponent(s) sacrifice(s) a creature it triggers Kalitas again, repeating the loop until your opponent(s) have no creatures left.