They can even rely entirely on X mana costs
Even if Vivi is not the focus of your Commander deck, exiling it with Agathas Soul Cauldron also sets up game-ending scenarios
You can also slow things down for your opponents by tapping Archelos, so that only you get the upside during your turn, and you can do that by using cards like Cryptolith Rite, convoke spells, or some auras or equipment that requires you to tap a creature
Ardbert, Warrior of Darkness Ardbert, Warrior of Darkness encourages you to cast white and black spells by handing out +1/+1 counters and useful combat keywords like vigilance and menace to your whole legendary squad
This is a little tough to cast because of Double-Green Double-White, but it is absurd if you can
(They each put the top card of their library into their graveyard.) Legendary Creature - Human Knight Drain (CTRL to add secondary) Draw Draw (CTRL to add secondary) Land Land (CTRL to add secondary) Mill Consuming Aberration Consuming Aberration's power and toughness are each equal to the number of cards in your opponents' graveyards