Ayara and Yahenni on the battlefield (Ayara on the battlefield as Ayara, Furnace Queen).
An opponent's life total is higher than or equal to your life total.
Steps
At the beginning of your combat phase, Ayara triggers, returning Scourge of the Throne from your graveyard to the battlefield, and giving it haste until end of turn.
Declare Scourge of the Throne as an attacker, attacking an opponent whose life total is higher than or equal to yours.
Scourge of the Throne's dethrone ability and second abilities trigger.
Resolve the second Scourge of the Throne trigger, causing you to untap all attacking creatures and to get an additional combat phase after this one.
Holding priority, activate Yahenni by sacrificing Scourge of the Throne.
Resolve the second Scourge of the Throne trigger from step 3, doing nothing.