原文A player's "opening hand" is the hand of cards the player has after all players have taken mulligans. If players have any cards in hand that allow actions to be taken with them from a player's opening hand, the starting player takes all such actions first in any order, followed by each other player in turn order. Then the first turn begins.
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.