Tezzeret's Betrayal
A kill spell with a delivery system stapled to it, built for one very specific table: a closed preconstructed box where the planeswalker it fetches lived in the same product. As removal alone, five mana at sorcery speed to destroy a single creature is well below the going rate; this is a Murder priced upward, and the body of the spell is not the reason to run it. The reason is the second clause, a tutor that searches both library and graveyard for exactly one named card: Tezzeret, Master of Metal. That is the inverse of a Diabolic Tutor or Demonic Tutor, which trade flexibility for power and can find anything; this finds nothing except its dedicated partner, which means it is dead weight in any deck not built around that one card. The graveyard reach is the clause doing the real work. Because it digs into the bin as well as the deck, the planeswalker cannot be stripped by discard or pre-emptive milling before you ever draw it; whatever happens to the card, the tutor hands it back. The whole construction is honest about its purpose: clear a blocker, refill your hand with your finisher, and smooth the variance of a deck whose entire plan is landing one marquee threat as reliably as the box can guarantee.
