Wording changes:
"Contact with a Harpy can various diseases"
- Should add the word "inflict"
"Don't seem to be effected by the diseases"
- Effected should be changed to "Affected"
Minor errors:
- "they're omparable"
- "higher via Improved Inative"
- "As a 7th level Fighterb"
Sentences:
"Due to having a strength score of 10[5] they can at max push 453.592 kg)"
- I would change the structure of that sentence to: " (...) they can push 453.592 kg as their maximum". But that's nitpicky at best, so you can ignore that.
"While Harpies are below human intelligence when it comes to academically they're highly skilled in lying, intimidating and preforming on stage"
- Simple wording change: "(...) when it comes to academics, they are highly skilled at lying (...)"
"When uttering a command the covered in ice and its hits deal cold damage on top of its regular damage[8]."
- Should say: "(...) the bow gets covered with ice (...)"
"A potion which upon consuming will grant the effects of the Cat's Grace which makes one more agile and coordinate[9]."
- Add that "Cat's Grace" is a spell.
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Aside from those minor errors, good job.
Something I'm starting to notice. We don't have references for the Nonphysical Interaction, particularly the nonexistent part (which should also get revised as a whole due to the new standards). But that's for a later time.