Who you are constantly runs toward who you will be. 

Mirror Mockery is on one level just another bulk rare with great art from one of Magic's best (relatively) recent blocks. It's an adaptable two-drop - at once an answer to attackers, a removal option against aggressive decks, and an engine to repeat your own ETB effects for value - but it's not that useful until later in the game most of the time, and running more than one copy in a midrangey, creature-heavy deck like this would get clunky. 

But I'm very happy that this list gets to run that one copy, not only because it's really effective in the deck but also because I think it (mechanically and in flavor) captures something really subtle and fundamental about blue. Blue is uniquely inevitable. Red bursts out of the gate and loses speed fast, white's control eventually crumbles as other colors outstrip it in value, green has tons of mana and nowhere to spend it once it's low on cards and creatures, and black expends too many of its resources to sustain itself in the long term. Blue, on the other hand, only gets likelier and likelier to win the longer the game goes. Blue is the slowest color in Magic, but it's also the most powerful. The reason blue is present in the vast majority of control decks is the same as the reason blue is the only mono-colored control deck: its characteristics lend themselves perfectly to a strategy that prioritizes answers early, keeps its hand healthy through the midgame with card advantage and selection, and gets out its big threats later on to overwhelm an exhausted opponent and win. Blue develops a vision for victory - "who you will be" - in the deckbuilding process, and expects its pilot - "who you are" - to employ the deck's resources with creativity and deliberate focus to get there.

"My time will come, when the rising tide will surge above the tallest mountain."

Mirror Mockery isn't the only two-drop enchantment in the deck, of course. Omen of the Sea is one of the best-designed blue commons for non-rotating format play in a while, and this list is happy to include two of them. Its flavor is perfectly servicable, with striking artwork, and I especially appreciate that the quote in the flavor text isn't explicitly attributed to Thassa; the god is an iconic character and doesn't need a "- Thassa, God of the Sea" for you to know that this line is from the big fish herself. That being said, I feel like Omen's flavor falls short of Mirror Mockery's. They're both trying to communicate similar things about blue, but Omen of the Sea demonstrates a self-referential tendency common to the Pioneer era of Magic, whereas Mirror Mockery harkens back to the game's early years by illustrating a scene that - while unmistakably set on Tarkir - doesn't require the reader to know about specific characters like Thassa to understand. Someone unfamiliar with Magic might be intrigued by Omen of the Sea - who's this blue lady and what's her deal? - but Mirror Mockery delivers a beautiful piece of art and a simple, poetic line of flavor text that resonates with everyone and consicely communicates the essence of blue at the same time. 

But Mirror Mockery doesn't lose sight of its place in the game. Tarkir is one of Magic's most beloved blocks not only because the concept and setting are, frankly, sweet, but also because it's a triumphant example of how a trading card game can make a genuinely meaningful point about life. For players familiar with the game, Mirror Mockery is not just a poignant observation about life but a meditation on Tarkir's deeper themes of destiny and change - themes that blue specifically is beautifully equipped to explore. It's not as explicit about it as the block's choice cards - Crux of Fate, for example, or the Siege cycle (of which this deck is happy to run Monastery Siege) - but those, while dragons fighting each other and/or Central Asian guys with magic powers is sick as hell, do expect a kind of familiarity with Tarkir that Mirror Mockery does not assume of its audience. The enchantment's contribution to its block is profound, but it works just as well as a standalone piece of art, and that's getting rarer in Magic these days.

If you're still reading this, thank you! I know this isn't a traditional deck writeup, but I think Mirror Mockery captures devotion to blue as an idea better than I could in a description like this. Plus, you already know Cavalier of Gales is a good card. It's a 5/5 flier for 5 that casts Brainstorm for you without a card whenever it enters the battlefield; of course it's good. You already know Thassa, Deep-Dwelling and Master of Waves are good cards. You already know counter magic is good, and card advantage, and flash, and creature control. They're the reasons devotion to blue is a great deck. I thought it might be a better use of my time, and yours, to talk about a 50-cent rare that doesn't get as much love, because I think it deserves it.