One tip against Omni-Tell is to hold 3Sphere in your hand. Never try to cast it for fear of counters. Their only way to win is through Show and Tell usually, so just wait to drop it off of that. Their lists vary, so be aware that
Dream Halls is a thing and that it costs 5 mana and keep an eye on their lands. I feel that trying to aggressively going for a Settler plan would be correct in this matchup if you can, otherwise try to kill then ASAP.
Edit: Sneak Show is a pain in the ass. Bridge is your best friend. I also bring in an Emrakul of my own to try to live the dream (which I have). I tend to ignore Sneak Attack and focus on messing with Show and Tell. Dropping Moggcatcher off of SaT can let you fetch up Stingscourger on your following turn to bounce their threat, so it might not be correct to run it out too early.