MTG Combo: Grave Pact + Parallel Lives + Spawnsire of Ulamog
With this combo you can force every other player to sacrifice all of their creatures. Parallel Lives doubles the number of tokens created when you activate the ability on Spawnsire of Ulamog. Since you can sacrifice those 4 tokens for the 4 mana necessary to repeat the process, you can see how Grave Pact can be oppressive.