If Blue, Loyal Raptor and Owen Grady, Raptor Trainer are your commanders, your deck may contain cards with green, blue, and/or red in their color identity, but not white or black
If you have a card in the deck, you can immediately use it
While we could still win the game normally by milling our opponent bit by bit, in this matchup, each card we mill is potentially game winning because if we ever mill the single copy of Approach of the Second Sun, it's almost impossible for our opponent to win the game
Once there, cards like Mass Driver were used to do Burn damage to your opponent's Life Points until they had no more
Snapcaster Mage has never been that good in straight UW, so it was an easy cut
As much as I want to dislike a verbose host without any vowels, the no max hand size and good toughness make this a great card