Oops, All Spells is a pure combo deck that wins by milling itself with Undercity Informer or Balustrade Spy, then reanimating Narcomoeba and Boggart Trawler to flashback Dread Return on Thassa's Oracle. Leyline of the Void in your opening hand shuts off Dread Return entirely by exiling the graveyard, and Containment Priest prevents Narcomoeba and Boggart Trawler from entering play through their triggered abilities. Deafening Silence prevents them from casting multiple noncreature spells in a turn, which cripples their ritual chains and disrupts their ability to set up the combo in a single turn. Your existing Thoughtseize and Cabal Therapy are excellent here to strip Undercity Informer, Balustrade Spy, or Pact of Negation before they can go off. Voice of Victory and Hexing Squelcher come out as their triggered abilities and combat-oriented utility are irrelevant in this race against a non-interactive combo deck.