Sorry to dig this old post up again, but...
I think this "abilities" idea could be very good. However, I don't think it should be 2 abilities per element. In fact, I don't think abilities should be element-related at all. I think there should be 12 generic abilities, represented by icons as SG suggested.
Or, maybe there can be some generic passive abilities, and some generic active abilities.
The bolded names in the below list are icons.
Sword: All your creatures have 50% to gain +1/+0.
Shield: All your creatures have 50% to gain +0/+1.
Flame: All enemy creatures have 50% to gain -0/-1.
Frost: All enemy creatures have 50% to gain -1/-0.
Cloud: Attacks against you have 10% to miss. This can cumulate with other card effects.
Mirror: When you're attacked, 10% of opponent being dealt the same damage.
Biohazard: When your opponent summons a creature, 33% of it having 1 poison immediately.
Skull: Your opponent start with 3 poison permanently, cannot be purified.
Cross: Each turn you regain 3 HP.
Tree: Your creatures regenerate 1 HP per turn when damaged.
Bat: You receive 1 HP per 10 damage dealt.
Sun: Nullify your opponent's ability.
Enemies starting from Elder Elementals will have special abilities. You will choose your ability when you defeat your first Elder, and after that you can switch abilities for 100 electrums.