This card is an iteration of Ragavan, Nimble Pilferer , a legendary creature that, whenever it deals combat damage, creates a treasure token and exiles the top card from your opponent's library, allowing you to play it until the end of your turn
Black follows with four, and blue has just one, Saiba Cryptomancer
For just two mana you get a solid removal spell, blowing up any creature with a power three or less
River Song The draw-from-the-bottom thing isnt actually what interests me the most about River Song
But for only 1 mana, that card is going to be the best, highest quality card your deck has to offer, possibly netting you a lot of card advantage through a board wipe, stopping someone else from doing the same to you with a counterspell, or setting you up to complete an infinite combo