Nightbird's Clutches

A Falter effect has never been complicated: take the two blockers in front of your attackers out of the equation and the damage gets through. The flashback is the wrinkle that elevates it from a one-shot trick into a recurring finisher. The first cast costs two mana and pries open one turn; the flashback costs four and pries open another, usually the turn the defender has finally committed enough bodies to feel safe behind them. Like every "can't block" spell, it has to be cast before blockers are declared, so you commit to the swing while the defender's plan is still hidden; the certainty you buy in exchange is absolute, since two creatures simply cannot stop the attack no matter how the blocks would otherwise have shaken out. The "up to two" framing also lets it clear a single key body when there is only one worth answering and the second target isn't worth spending. This is a closer wearing a combat trick's clothes, built for the aggressive deck that wants to convert its late-game mana into lethal rather than into a fresh threat off the top: the same effect, sold to you twice, exactly when an emptied hand needs the board itself to finish the job.