Overview
I enjoyed playing this game more than not. The game had strong points that encouraged me to explore deeper than my initial impression, and I didn't come across anything that completely broke my immersion or made me want to quit. I feel that this project generally succeeds when taking into consideration the time frame and objective, although the majority of the game's content is somewhat lackluster in a vacuum. However, there isn't much to dislike about what you added or the choices you made. In fact, I think you nailed most of the components down fairly well--it's just that there's too much missing from the game as a whole, and it sometimes came across as perfunctory. It seems to me that your idea was very ambitious and that you were ultimately forced to make a lot of concessions in a "race to the finish line." Having a grand idea and coming up short can be a reflection of a great attitude towards game development, however, as it's indicative of enthusiasm, goals, and a willingness to improve! Overall, I think you accomplished a lot here as a developer and I think you're moving swiftly in the right direction. Whether you decide to move on or continue working on this, it's a substantial accomplishment and something to be proud of, and I look forward to seeing what you make in the future!
Gameplay
The introduction was sufficient to get me started, albeit with a little extra effort on my part to learn how the enemies and ui elements behaved. The baseline for this game is a turn based battler, which I was very surprised to see from a solo dev in a 3 day game jam, lol. These games have a ton of moving parts and thus rely very heavily on a strong UI, which is imo the hardest game component to design and perfect. I encountered bugs and other seemingly unintended game interactions rather frequently, especially ones concerning the mutation tree and enemy behavior (if you decide to continue working on this project, I'd be happy to list the exact bugs I found and possible fixes for them.) The game is, as you noted, wildly unbalanced. I never once felt threatened, or even more than mildly affected, by any of the enemies I encountered. I only recall being hit once by a spit enemy for less than a tenth of my healthbar, and after I learned that enemies could do their spit attack, it was also trivial to avoid. The options and information provided to the player are overwhelmingly powerful. Being able to freely skip turns to utilize zugzwang* makes the player almost invincible (*if you aren't familiar with this, do yourself a favor and look it up, it's a major concern in turn based games like this.) The enemies aren't threatening, aggressive, or unpredictable enough, and they'll even clear themselves out if you just stand there and do nothing. This is something I'd definitely recommend focusing on if you continue with this game. Enemies should be scary! Give them global range attacks. Let them run around the map and deal massive damage out of nowhere. As long as you give the player enough control to make meaningful gameplay decisions, less deterministic interactions would really breathe a lot of life into this.
Theme
I'm running out of room so I'll keep the next sections somewhat brief. I liked your interpretation and I think it fits well into the rest of the game. Besides bugfixes and simple balancing, I don't think you need to make any major changes to the tree itself--I would, however, change the way pickups work, or at least make them despawn so the player can't just run away and come back when it's safe.
Aesthetics
Not much to comment on here. I think you did a well enough job with the little time you had for this, but I think you'd benefit immensely from working with a dedicated artist (and maybe another programmer responsible for things like UI) in the future.
Sound
My comments about art also apply here. If you haven't dabbled in music and sound design already, and if it isn't something you really look forwards to, you're better off working with a musician and putting your full focus towards development. It really sucks that sound, aesthetics, and theme are all their own categories, as it unfairly punishes solo devs imo. It also isn't as rewarding for people who take risks and try to make their games special, which is what game jams should be about. To balance this out, I've been giving no less than three stars for sound and two stars for aesthetics for people who clearly were not able to spend any time on them, so I gave you three for each.