Bro this reminds me of Ben 10 and you have no idea how big of a compliment that is.

I like this but it's too repetitive and I don't think really is anything like Undertale (I haven't played / watched the others) you have a great ear for what sounds you want and your mixing is impressive for the first track you've made.

Blue Lava has made some great suggestions already but in this genre I would consider fading in and out an instrument that plays like one note in sixteenth note patterns to add a little movement. More percussion also would help with the groove.

I think you did a great job at picking the sounds, instruments, and rhythms needed to achieve the atmosphere you were going for! I could totally see this as a BGM for the scene you describe. I did find the track to be a tiny bit repetitive in the later half, maybe you could try varying the rhythms and notes of your main musical idea to make it more surprising and fun to listen to there?

I like that you chose to use the Earthbound soundfont as there are a lot of unique and interesting sounds on there. It highlights the mysterious nature of the forest you are portraying. The arpeggiating bass feels almost disorienting as if you are getting very lost in the forest. I really like the xylophone sound at the end which has a low hollow sound but also a high-pitched attack which highlights the thunder part of the woods in your theme. If this is your first track ever, then I cannot wait to see what you make in the future! You have a good sense of the evolution of a song and even though there are some repetitive parts, the song still manages to change and evolve throughout. One suggestion of something you can try in the future is to add some movement with the harmony in your piece. Something that works in some ambient music is to take a loop that you’ve already written and move it down 3 notes. Then move it back to the original for an alternating vamp. This is a technique called the chromatic median and can allow for a sense of movement without making anything sound too resolved or “final”. You have a good ear for sounds and what fits well together so keep exploring and trying things out! Thank you for sharing!

The lead shifting to harsher distortion is a really cool moment. Overall, I enjoy that the composition isn't too static and you're adding or removing parts frequently in the second half. As for advice, I think some more bass would be nice in the more intense parts of the song, panned in the middle to sort of ground the arpeggios that are switching between left and right. Also, but this is up to personal taste, a bit more percussion for example a kick and snare. This would give it a more consisten groove, so I also understand the decision to omit them for a more disorienting piece.
I like it :)