Soul Warden: Our resident bat lady! I originally overlooked her because I wanted all creatures to be bats, but adding so much life gain and being a one drop became too tempting. She gains life early to help us stay alive, and adds to the life loss for our opponents once we have a Starscape Cleric or two in play.
Ajani's Welcome: Basically the same as our Soul Warden, but an enchantment. It's tempting to run Soul's Attendant as Soul Wardens 5-8, but that's too many non-bats. Admittedly, Ajani's Welcome can be disappointing to draw late game since it won't trigger Soul Warden or Lifecreed Duo but I kind of like the resiliency of it not being a creature and therefore a little harder to remove.
Lifecreed Duo: A two mana Soul Warden and it's a bat. Easy inclusion!
Zoraline, Cosmos Caller: This is where things can get wild. If we make it to the mid-late game Zoraline can end it very quickly with a couple of Starscape Clerics out. Since each bat attacking is a separate trigger for Zoraline each Starscape Cleric will trigger once for each bat attacking. This adds up very quickly and can often end the game before you even get to combat damage. Having 4 of a legendary isn't always great, but I find in the games I have an extra Zoraline stuck in my hand I'm usually much happier than in the games I don't have one in play or in my hand.
Starscape Cleric: This is what it's all about. Just one of these can end the game over a couple of turns. Multiples can end it the same turn they come down. The fact that it has offspring is mind blowing and game ending. Sure, we can end the game with flying attackers, but this guy makes sure it usually doesn't come to that.
Aether Vial: Another great turn 1 play. This one helps us power out creatures even faster, get them into play on our opponent's turn, and sneak around counter spells. By virtue of the existing bats (and some natural selection) most of our bats have a CMC of 2. The first Vial should always be on 2 and if you have a second put that one on 3.