Free Essence/Vigor
Okay, not "free" as in "unlimited". Rather, eliminating it from the card pool, partially anyway. My suggestion is to go the route of Pokemon TCG Pocket Energy and allow BASIC essences to be gained for free, with some caveats/modifications.
So Pokemon TCG Pocket makes energy its own spot with a guaranteed one at the start of each turn (except the very first). If a deck uses more than one energy type, the type is chosen at random. You can also see which energy will be given to you at the start of your next turn.
What my exact suggestion is would be to do the following instead. We have a spot for drawing "a new essence". That essence will be the equivalent of a basic essence card as they are now. Like Pokemon TCG Pocket, we can see what the current one is and the next one that will be available. However, we still have the advanced essence cards as well. In keeping with the 1 essence limit, playing those cards from the hand will consume/exhaust the essence card that's presently available to be activated.
By doing this, we can reduce the deck bloat that is essence draws and speed up the game a bit without totally sacrificing "which essence should I use?" Characters may even want to forego the free essence to make use of abilities (like Cinder as she is now). We can also make this a mechanic that's based on the played character, where certain characters can only generate certain essences. While it would somewhat restrict deck building, it adds a degree of strategy as well because certain advance essence cards could bypass that restriction as well.
Marigold's Ability
Right now, it's very unsatisfying and needs massive setup to do anything meaningful. Needing followers to do damage is just far too much of a handicap. And Cinder's clearing whatever followers Marigold can put up far too easily (a critique I've brought up before).
My suggestion is that she can swallow (exhaust) an enemy Follower that is smaller than she is and gain a portion of their size when swallowed.
Since her style is to keep growing herself and her followers, it makes a lot more sense to make her more of a threat the bigger she's allowed to get. This changes her ability from a 4 Vigor 1 damage (worst case scenario, which is too often) to "I can eliminate any follower if you don't win quickly"; reinforcing her intended play style. Naturally, this would come at a higher vigor cost (my suggestion is 6 vigor 2 Green).
Some better cards for Marigold
This is partly because of the disparity I see with Cinder regularly nuking Marigold's followers far too easily. I know you plan to add more anyway, but for the sake of "give Marigold better odds", I think she needs a few emergency cards swapped in so she can keep up with Cinder's nukes.
- A Boa Lamia, a massive version of the Garter Lamia. Preferably with the ability to grow by absorbing a follower it defeats and recovering Lilumi in turn.
- A structure that recovers Lilumi and grows Marigold.
- A Talisman to reduce physical damage based on size.
- A Talisman that grows all followers present when played.
- some more draw power (Cinder literally has more and better draw cards)
Something for if/when the deck runs out
This can be something to help end the game, like stacking exhaustion. Or it can be "shuffle the exhaust into a new deck" so things can keep going without rushing. I think "end the game" is probably more favorable, but it is something that needs to be decided on, even though it's not really an issue currently with where the game is.
So.... I managed to pull this off... I had triggered a teleportation secret in Level 5 that lead back to the starting elevator, but the elevator wasn't there. I walked off and.... This.