結界
每當你犧牲一個生物時,你可以將目標魔法力值小於它的生物牌從你的墳墓場橫置移回戰場。每回合只能如此作一次。
“Do this only once each turn” refers to returning a creature card from your graveyard to the battlefield using the triggered ability. As long as you haven't yet chosen to do that this turn, all instances of sacrificing a creature will cause Riveteers Ascendancy's ability to trigger.