Cut Your Losses

Mill-half is a scaling effect, and the tension every "mill a fraction" spell has to answer is that it does the most work when the target's library is fattest and progressively less as the game runs long. This one leans into that curve rather than fighting it: as the biggest single fractional mill blue offers, it wants to land while the deck is still deep. The Casualty tax is where the design gets interesting, because the copy does not double the effect the way a flat-number spell would. One copy mills half; the next then mills half of what remains, so two hits clear three-quarters of the library rather than all of it. The rounding-down clause guarantees this can never finish the job on its own: half of a shrinking pile always leaves a smaller pile behind, and no amount of copying reaches zero. That makes the spell a fast opening or midgame blow to a deck's foundation rather than a clean kill, one that still expects graveyard payoffs or a follow-up to convert the head start. And the tax points the card toward boards that already have a body they can spare: a creature with power 2 or greater is the entry fee, so sacrifice-friendly shells pay it more comfortably than a control deck reluctant to give up a blocker. Blue's premier mill effect is quietly a card that rewards having creatures, not a card that replaces them.