Obviously at the top is the Iris, which mutated or maybe invaded Neptune to better get access to the solar system.

Next are the Gardeners, which make sure that the gardens or nests are maintained and free of intruders.

Then there are wood crawlers, and my theory is that they are the original of their species that came from the gardens, which take vessels but can either use them as vessels, or use them to plant Nature’s Mockery, which will sprout into either Skin walkers or Wood Crawlers. I haven’t caught any distinction between the two aside from names but I would say they sprout into Wood crawlers as we see the legs of one with the caption Nature’s Mockery in the first video. Perhaps the skin walkers would also be something like what Mary is. It’s hard to say as she’s one of the only few with a human name and an appearance, but no name on what she is, just what she’s associated with.

So essentially the skin walkers/wood crawlers come and infect you with “Deep Root Disease,” which if left on for too long will consume you slowly, turning you into nature’s mockery and maybe even connecting to the gardens, which will turn you into a wood crawler to repeat the process. I would think there’s a different method for the gardeners but they may have also been the first ones on the planet as they got beamed down from Neptune. Obviously though their goal is to wipeout the humans and infect or “mutate” earth as well. There’s no real telling if it has interest in the other planets and is wiping out earth as it’s the most resistant and used Neptune as the “lens” through the “gateway” to skip there, or is just interested in earth only and did the process as mentioned above to bypass the other planets while having a reliable planet in the solar system (Pluto could work but it hangs out on the edges too much, what a loner)