One of the new mechanics added in the Rising Tides Expansion is drawing cards from the enemy's deck. These three cards are all widely used for their ability to pilfer cards from your opponent.
Yordle Grifter is the Allegiance card for the Bilgewater region, which is often worth playing just for the free copy of Warning Shot that it creates — this is an easy way of activating Plunder effects.
Pilfered Goods is the star of the show, here. It's a 2-mana spell that can reliably steal two cards off the top of your opponent's deck. What's not to love?
Black Market Merchant has a nice effect on its own, pilfering one card from your opponent if the Plunder condition is met. Combined with either of the other two cards in the package, though, and you start to generate some crazy value.