What do the first two have that the third one does not? Flash, of course. I was thinking of all the hits I have taken from Snapcaster Mage and Vendilion Clique, and all of them have one thing in common: they all happened at a time in the turn when the only way to make a play with a creature is for it to have Flash. With Flash, you can sit there waiting for just the right moment. You may have even played a spell that let you see your opponent's hand, and then you swing with Vendilion Clique and take out the offending card. It's a sweet play.
Now enter our new card, Thought-Knot Seer, which you can see coming because it can only be cast at the beginning or at the end of a player's turn on their turn. Never mind that it's a four-drop. That extra mana makes a huge difference between Vendilion Clique and Thought-Knot Seer. Oh, and did I forget that Vendilion Clique has Flying?
It is true, though, that Thought-Knot Seer is not blue. But it is also not generic like Wurmcoil Engine. You need a way to cast with Wastes. Still, I think Thought-Knot Seer is worth testing in Modern, yet I would like to test it in decks not running blue, since these are the only decks where Thought-Knot Seer adds something Vendilion Clique cannot add.
