This guide is great, I wish I found it earlier, but its been amazingly helpful.
I started out with air, then added some life cards and got muy rare, I chose the Owl's Eye and upgraded it to Eagle's Eye.
I was relying on Queens to produce Fireflies, and Rustlers to convert light to life, and Emphatic Bonds to heal me. This strat had me struggling with level 2 matchups.
I got annoyed and started selling off the cards, including the Eagle's Eye and built up a fire and darkness deck. Now I have removed a bunch of cards so its mostly a darkness deck with a touch of fire.
15x Obsidian Pillar
5x Black Dragon
3x Steal
3x Ash Eater
1x Brimstone Eater
1x Fire Spectre
1x Immolation
1x Photon
With that I'm finally able to win against level 3, and very often too! I keep the Photon in there just as a cheap sacrifice for the Immolation card.
I'm sure my deck still isn't the best, but this guide allowed me to use the cards I already had, in a new way to drastically improve my win rate. In the time it took me to afford my first upgrade, I'm now able to upgrade 3 or 4 cards, depending on how the spins go.
So thank you very much for writing this up.