mtg wither cards Withering Torment (DSK-124) Uncommon Artist Withering Curse 105 NM Secrets

For Death's Shadow, the average converted mana cost is incredibly low (likely the lowest in all of Modern) at 0.76, meaning the average nonland card in the deck costs significantly less than one mana

So, satisfying the historic requirement and can reasonably get the second ability off

You can usually afford to lose your most marginal spell or a land

Once youve cast one version of Extus, any additional copies you draw can be used to either recur sacrificed creatures or to create another avatar token to wail on your enemies

You can cast it turn 3 (or turn 2, with a dork) to claim the monarchy before your opponent can contest, or you can dump all your mana into it turn 8 to win with a hasty cavalry