Containment Priest is not a good fit here, so this plan makes no swaps. Priest only exiles nontoken creatures that would enter without being cast. The Cat tokens from Ocelot Pride and Ajani, Nacatl Pariah are tokens, so they still enter and the engine keeps running. Against this deck Priest is just a 2/2 flash body, and it does not justify cutting anything from the main deck. Their game plan is cheap creatures backed by Swords to Plowshares, Static Prison and Goblin Bombardment, so keep the main-deck interaction (Swords to Plowshares, Kozilek's Command, Eldrazi Confluence, Force of Will, Force of Negation) and rely on it to answer Ocelot Pride and Ajani before they take over. Be aware that their sideboard has Null Rod, which would shut off our artifacts' activated abilities, and Pyroblast, which can counter or destroy our blue spells and permanents. Karn's static ability has little to do against a main deck with no artifacts, but Karn is still a fine source of card advantage, so it stays in.