This is my take on a tempo/midrange deck that looks to control a bit of the early game and then hit its own high-value board-presences.
Advantage
Sin Prodder - A 3/2 menace for 3 is an okay body but the "punisher" mechanic is extremely valuable. It won't run away with a game but its either an extra card on up keep or burn. (Note: it's not a strict punisher because the card still exists outside of the decision and repeats on upkeep as opposed to something like Vexing Devil).
Nahiri, the Harbinger
- This is a real tempo card in the deck with each of her abilities. Her plus provides card advantage (and is optional if you don't want it). Her minus is great board control and her ult can finish off a game.
Game Changers
Archangel Avacyn
- This is my favorite card in the deck. 4/4 vigilance flyer that you can flash in with "all creatures are indestructible on ETB" is absurd. But then she flips into a 6/5 flyer, board clears and burns to the face.
Archangel of Tithes
- I still don't understand how she isn't Legendary. Horrible to defend against and an even better defender herself. Casting spells for your opponents becomes a lot riskier when she's on the board.
Gideon, Ally of Zendikar - He is always a threat and can be a finisher or provide steady board growth. Just so much value for 4-mana.
Secure the Wastes - You'll find a lot of value with this card, both as a win-condition with Westvale Abbey
as well as stand-alone. It's great defensively or offensively with it being an instant and flexible on the mana curve.
Board Control
Declaration in Stone
- Really solid removal here with the exile. Excellent against tokens or weenier decks that like to drop several of the same creature. Giving up a clue would be problematic if not for our own potential for card advantage.
Fiery Impulse
- Excellent against more aggressive decks. It's what you want to use against
Thalia's Lieutenant
and the like.
Exquisite Firecraft - It's real value is in its flexibility. It'll clear difficult creatures or it can provide that final few points of damage for the win.
Stasis Snare - Another exile mechanic that can remove any creature. More expensive than the dec in stone but you're not giving up a clue and Flash beats Sorcery.
Conclusion
This is my first approach to something not Ramp so I'm sure I'm missing some basic cards or mechanics that provide clear tempo advantage. All suggestions and constructive criticism appreciated!