Some notes:
“Duplicate the last ingredient you obtain” includes ingredients obtained via duplication. The potion adding echo takes effect afterwards. So, if you have a “duplicate the last ingredient” ingredient followed by a bunch of blank spaces, it’ll activate, making a copy of itself in the next space, with some echoes added. Then the next one will activate several times, making copies of the newest one, adding more echoes each time. With some potions for extra ingredient slots, and some potions to add echo at the start of the round, you can easily get an herb with dozens of echo activations attached in one round, along with a bunch of herbs to sell for money. (You can also get lots of money from the potion that gives a chance of money for each activation.)
Now, sell all but the most echoing “duplicate the last ingredient” plants, and then buy a “duplicate the last potion” (rosemary). Then make sure your last purchased potion is “add echo to a random ingredient at start of round”. Within one more round, you can get many copies of rosemary with increasing numbers of echo activations attached, and get a massive number of bottles of one of the potions that add echo.
This results in an exponential amount of echo, growing proportional to the Fibonacci sequence.
Throw in a Traveler’s Herbal Tea to get stars per activation.
Currently partway through a very long scoring, getting thousands of stars per plant activation, getting a couple of gold per activation, and each plant is activating an absurd number of times. Waiting for the scoring to finish so I can see how much echo I have. And I’ll have thousands of gold to search the shop with for the next round.
Also, my first ingredient slot seems to be bugged and not activating, possibly related to dragging things around while there’s overlap between bottles and ingredients.
Update: At end of round, the best rosemary had echo x415.