Here´s an idea I had last night:
Aether creatures are immaterial (which means that they are immortal, too) , but Quintessence gives only Immortality.
The difference will be the following:
Immaterial creatures can´t drink potions, immortals can,
so you can use potions (alchemy cards) on immortal creatures, which are not immaterial.
Imortals stay immune to spells and skills, but not to alchemy cards.
That could give new ways of using potions.
You can use Liquid Shadow or Aflatoxin on an immortal Oty, but not on Phase Dragon.
I didn´t think much about balancing, we could do it here, but i thought I should post this.