You have sacrificed at least three artifacts and/or creatures this turn, plus an additional artifact or creature for each time you've cast Dargo from the command zone this game.
({R} magic symbol) available.
Steps
Cast Dargo from the command zone by paying ({R} magic symbol) .
Birgi triggers, adding ({R} magic symbol) .
Activate Yahenni by sacrificing Dargo.
Choose to return Dargo to the command zone from your graveyard.
Resolve the Yahenni ability, giving it indestructible until end of turn.