Thwart the Enemy and Obscuring Haze You know what
Since the card is currently only being played in just one modern deck, I personally had it in the third spot behind the best blue reactive spells in the format, Counterspell and Force of Negation, but I can see the number one spot going to the best and most efficient threat the color has to offer
That's what happens when you combine Tinker (which could get out the Jar almost immediately) with Megrim (so that your opponent would take 14 damage from a single Jar discard, assuming they could not play any cards in time)
This is one of the best and most extreme implementations of sneak, but it takes the card from being a possible inclusion to a must-have for milling decks, and maybe even at three or four copies, too (in Standard)
At face value, it seems like a good Limited card, which it is