I am LOVING this game. No surprise since I love all of your games, but blending my two favorite genres of incremental and deck building? -chef's kiss- Delightful!
I do have a couple of notes. One, I noticed the "Reduce Energy Cost" upgrade for the mage states "Reduce cost by {amount}."
Secondly, this may be a #skill issue but I feel like the Mirror runes don't synergize well for me. There's quite a few runes that seem to work best playing earlier in the hand, so doubling them early can be really beneficial. But it's other rune to increase light earned by 20% this round is best to play last. Perhaps the amplify rune can take effect once the entire hand is played? Or the mirror effect can be used on the next card regardless of turn? Just some thoughts.
Anyway I can easily see myself playing this for hours on end! You just say the word and I'll be ready to toss money on this game (or any of your games) to own it. :)