Blasphemous Act is a nine-mana red sorcery spell that deals 13 damage to every creature in play. That sounds like it’d be far too expensive, but it becomes one-mana cheaper for each creature in play. That means it can be as cheap as just one red mana, and one red mana is an incredibly low price to pay for removing every creature in the game. There is a variant of this effect (but in black) called Blasphemous Edict, which is also rather good for Commander.