Main Goal of the Deck:

Get as many creatures on the board as soon as possible pass damage and be done by turn 6. Aethersphere Harvester is a flyer that gives you the ability to attack when the opponent has bigger creatures and also synergizes with Crested Sunmare on turn 5 and later by getting lifelink.

Additional Synergies:

Enchantments such as Arguel's Blood Fast and Legion's Landing are doing things such as drawing cards when you might need them and placing Vampire Tokens with lifelink for either crew or Crested Sunmare, Although Arguel's Blood Fast is not so valuable in the early game, it can be a massive booster on late game, giving you the ability to sacrifice a creature to gain life equal to it's toughness. That synergizes really good with a horse, since you'll be sacrificing one to get one, you'll end up in starting life in no time.

End Game:

The thing here is to get the opponent to 0 as soon as possible, if you fail to do so, Crested Sunmare is a safe way to win providing you passage to indestructibility with only one true enemy: Hour of Devastation.

Changes:

I removed the 1-drops Vicious Conquistador because they where dead cards after turn 1. So basically only good when you had them as starting hand. Instead I chose to play Adanto Vanguard which is great against control, because he gets indestructibility at instant speed just by paying 4 life, and with all this lifelink I don't care much.