The game state is the one in the attached image. You know the opponent has a drowner in hand and a blessed alliance, from when you tidehollowed.
Here's what I did:
Attack with thought knot. Wait for him to blessed alliance, then vial in flicker, flickering my thought knot. This lets me take the drowner, which won the game.
This kind of situation is why the only deck I'll ever play in modern is taxes! Just switched from GW (which was 54-30) to E&T (which is now sitting at 32-14 in leagues). I'm super pumped for concealed courtyard, I'll probably drop the two vents and a plains and run 3. I realllly dislike the card shambling vent.