原文A power-up ability is a special kind of activated ability. "Power-up — [Cost]: [Effect]" means "[Cost]: [Effect]. If this permanent entered this turn, this ability's cost is reduced by this permanent's mana cost. Activate only once."
原文If you activate a permanent's power-up ability on the same turn that permanent entered, the cost of the power-up ability is reduced by that permanent's mana cost. For example, say you want to activate the power-up ability of Aerial Doombot on the turn it enters. Aerial Doombot's power-up ability costs 5 . Since Aerial Doombot's mana cost is , it would cost only 5 to activate that power-up ability that turn.
原文Some power-up abilities require targets or have optional targets. If one or more targets are chosen for a power-up ability and all of those targets are illegal as the ability resolves (usually because they left the battlefield in response), the ability won't resolve and none of its effects will happen. However, since the power-up ability was already activated, it can't be activated again.