原文To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
原文"Do this only once each turn" lets you choose whether or not to have the Villain connive as the triggered ability resolves. If you don't, the ability will trigger again the next time the condition is met. Once you choose to do so, the ability will no longer trigger for the rest of the turn and any other instances of the ability that have already triggered and are on the stack won't have any effect.
原文Once an ability that causes a creature to connive begins to resolve, no player may take any other actions until it's done. Notably, opponents can't try to remove the conniving creature after you discard a nonland card but before it receives a +1/+1 counter.
原文If no card is discarded, most likely because that player's hand is empty and an effect says they can't draw cards, the conniving creature does not receive a +1/+1 counter.
原文If a resolving spell or ability instructs a specific creature to connive but that creature has left the battlefield, the creature still connives. If you discard a nonland card this way, you won't put a +1/+1 counter on anything. Abilities that trigger "whenever a creature you control connives" will trigger.