Omni-Tell wants to Show and Tell a free Omniscience or Emrakul into play, so Containment Priest is the key answer, exiling any nontoken creature (like Emrakul or Atraxa) that enters the battlefield without being cast. Disruptor Flute naming Show and Tell taxes their key enabler by three mana, buying crucial time and disrupting their fastest lines. Keep Thoughtseize as your best proactive disruption to strip Show and Tell, Omniscience, or a payoff before they can deploy it safely behind Force of Will/Veil of Summer. Cut Boggart Trawler, Meteor Sword, Flickerwisp, Loran, and Emperor of Bones since they're too slow and irrelevant against this combo-focused plan.