Capitalize personifications such as Mother Nature.
How does one slightly exterminate all of something? How does one slightly exterminate anything? (See what happens once someone starts using decimate to mean destroy utterly?) Deleting all and changing the adverb to mostly would make the sentence work, though.
Change 1/3 to one third.
Misspelling alert: change excists to exists.
Combine fragment With varied… with the previous sentence and merge the list into the same sentence, using a colon to introduce the list.
Mother Nature has taken back her world and exterminated humanity… mostly. One third of the population still exists as some type of plant people, with varied features: mushrooms growing on their shoulders, skeletal remnants protruding, or sunflower petals for hair. You are one of these plant people.
(Y’know, kids, it’s this thinking of “Mother Nature” as something totally separate from humans that lead to humans mistreating nature in the first place. Are humans somehow unnatural, then, rather than a part of the world we live in? *rolls eyes*)