Many seem attracted to the dream of curving Woodweavers Puzzleknot into spiking an Ulamog, the Ceaseless Hunger on turn 4, but I just dont see building your deck in that manner as a realistic path
Black Cat, Cunning Thief Black Cat, Cunning Thief is more expensive than Gonti, Lord of Luxury and lost its deathtouch but looking at 9 cards and getting two is still quite good
Then, it has both trample and hexproof, ensuring that at least some damage is going to slip through your opponents defenses, and making it awfully difficult to remove outside of combat
Dont forget that Adarkar Valkyries ability can be used to take control of an opponents creature if its going to die and would do some work on your side of the battlefield
This card basically gives you an entire half of a new hand for almost free, and I cant think of a better way to climb back into a game or pull ahead of your opponent than casting this card