Izzet Spellementals relies on filling its graveyard with cheap instants and sorceries to cut the cost of Hearth Elemental and Eddymurk Crab and to power up Flow State, so Rest in Peace is devastating. It exiles their graveyard and keeps new cards from ever landing there, which shuts off those cost reductions and Flow State's bonus. Voice of Victory is excellent here too, since your opponents can't cast spells during your turn, which stops them from responding with instant-speed cards like Opt, Burst Lightning, Prismari Charm, or Get Out while you attack. Doc Ock's Tentacles and Basilisk Collar are cut because this matchup is about denying their engine and racing, not grinding incremental value. Raubahn comes out since his ward tax doesn't matter much against a deck with little hard removal, and the slot is better used proactively.