Now I have only been playing since the beginning of the year. So don't take my word on this. Try Renting the cards before buying.
I have found what I think is the best play for 20 Mana. Now the only problem with this build is you need a guarantee 20 Mana for battle.
First you need a LVL 2 Tarsa Can be bought for around $15.
Second you need Antoid LVL 3. He will be your tank. With the Shield that will reduce incoming Ranged and Melee attacks. Does NOT help against magic attacks. This is ranging around $2.
Third is the Ant Miners. He has Scavenge. When his cards die or one of your cards dies. This card will gain one health for each card that dies. Good for a back up tank. This is going for $2.50.
Fourth will be the Kobold Miner. This card has a favorite move of mine called sneak. Sneak will allow the card to attack the last card in play. Card is going for roughly $8.
Fifth card in this will be the Serpentine Spy. Now this card is a little pricy so I rent this one right now. Its worth around $22. This as the awesome ability that is called Opportunity. Opportunity goes for the card that has the lest amount of health at its turn. Great for when Kobold and Tenyii start going after everyone. AWESOME!!!
Sixth Card is the almighty Tenyii Striker. Ability is Sneak. And only $2.50 for the card.
The final and Seventh card for this build will be the Scorch Fiend. This card will act as a shield for Tenyii. Thats why Scorchs are our fiend. Also the best part is it costs 0 mana to play. This card has went down roughly $1.25 since I been playing. This is around $4 now.
The total cost of this build is a little under $60 from the time of writing this.
Now I shall buy slowly and LVL Tarsa to LVL 3 hopefully I can get this deck upgraded by July.