Morkrut Behemoth

The additional cost is the whole design conceit here: this is a 7/6 with menace whose printed cost sits below rate, and the extra tax is how the card is kept in line. Feed it a creature and the body lands for five mana, a genuinely oversized threat a turn or two ahead of the curve, which is why the sacrifice line is the one the card is really built around. Pay the instead and you have paid a full seven mana for a 7/6, an honest but unremarkable rate that exists mostly so the card is never dead when there is nothing to sacrifice. That is the trade the design is asking about: a deck stocked with expendable bodies converts a spent token or a used-up utility creature into evasive power, while a deck without fodder still has a fallback. Menace does the closing work on both plans, since a 7/6 that demands two blockers is hard to trade against profitably and harder still to chump twice. It sits in the long line of black top-end that leans on a strings-attached cost: a big evasive finisher priced for boards full of sacrifice fodder, but with the pure-mana escape hatch that keeps it from folding when the board is empty.