Hi, thanks for playing! Take your time with it. Serenitrove is meant to be a chill and relaxing journey, though you can totally hardcore it if you want to ;)
My favorite turtle is probably Caelo. The most difficult ones to implement code-wise were Fern and Reeler. And yes, there are a few turtles that were set aside, not really scrapped but put back on the drawing board for more balancing and planned for future updates.