结界
在你的维持开始时,你可以选择目标由你操控的非地永久物,与目标由对手操控、且总法术力费用等于或小于前者的非地永久物,并交换它们的操控权。
Even if you don’t plan on exchanging control of any permanents, if you can choose two legal targets when the ability triggers, you must do so. If you can’t, then you don’t choose any targets.