Alright, cool.
Well, looking at each element, we should avoid making strong mono cards rares, and instead make them cards worth earning, but at the same time, cards that aren't vital. For instance, graboid is a great pick. At the start of the game, when earth doesn't have extra marks or off-element cards, they wouldn't be able to use graboids effectively.
But at the same time, this looks completely unfair for life. Looking at War #2, graboid rainbows are one of the most effective decks in the game, and I worry about the advantage this gives life. Still... if I had to pick...
![Aether :aether](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/aether18x18.png)
Spark + Phase Dragon = Immortal?
![Air :air](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/air18x18.png)
Azure Dragon + Firefly = Firefly queen
![Darkness :darkness](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/darkness18x18.png)
Devourer + Vampire = Parasite
![Death :death](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/death18x18.png)
Virus + Flesh Spider = Deathstalker
![Earth :earth](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/earth18x18.png)
Shrieker + Antlion = Graboid
![Entropy :entropy](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/entropy18x18.png)
Abomination + Maxwell's Demon = Fallen Elf
![Fire :fire](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/fire18x18.png)
Fire Spirit + Phoenix (Ash) = Lava Golem
![Gravity :gravity](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/gravity18x18.png)
Graviton Mercenary + Otyugh = Graviton Fire Eater
![Life :life](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/life18x18.png)
Life Dragon + Forest Spirt = Leaf Dragon
![Light :light](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/light18x18.png)
Golden Dragon + Guardian Angel = Pegasus
![Time :time](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/time18x18.png)
Scarab + Anubis = Pharaoh
![Water :water](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/water18x18.png)
Toadfish + Arctic Squid = Chrysaora
I tried to pick powerful cards, but at the same time, cards elements won't want until the reach higher levels anyway.