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Object invocation goes very closely to Wanderer, (into can be found here) but! If you make it a bit more clear in what exactly she can do w/ the object and what type and what this does for her. It's a perfectly doable thing, just please clarify what this means for her, (can she only go into gold? into a certain item, ect, how is her power tied to the object in question).

Personality: She cannot be part Siren. Cross breeds do not occur in halloween so sadly this is not doable. And only because I actually had this as my original plot, I will mention that my siren started out unable to sing. Not fully mute but was utterly unable to sing. So just be aware that that plot in particular has been done. If you wish to pursue it, that is up to you.

Her personality is also very sparse. All that is said about her personality is about external factors, nothing that makes her act and why. Is she shy? Is she depressed, introverted, a kind person, thoughtful? What you have in her personality is all about her physical self. Try to explain how she acts with others.
Like, how is she X, and how does this affect her relationships? If she is Y, how does that help her make friends, make enemies. Think about what makes her who she is on the inside, rather than the outside!

What I think your biggest issue here is the half siren thing. You will have to either make her a siren, OR, you will have to remove that entirely. :C
Her fear also doesn't really match up with her species, as the Enchanted Moura focuses on treasure guarding, beauty, and the ability to sing. So I would only suggest reconsider it maybe. Singing could possibly heal, cause pain, distort enemy accuracy, ect.

Fix personailty
Fix natural Ablility
Fix Fear

TiH allows for more than one of any species, so if you really want a siren it's totally do-able~ If you want to follow the Naiad path, they're associated with fresh water so maybe something like an ability to create a small amount to control for short periods, or maybe the ability to blend into any body of fresh water and become inherently "invisible" while there.

What makes Cosette stuck up? Is it because she's confident in her beauty and prowess, family being rich and awesome, or is it a facade she puts up to look "cool"? So far we're getting this really bitchy side, which insinuates she'll have issues making friends - what are her positives?

The naiad is a good choice for a TiHer! But then water based creatures are pretty rad in general |D

Natural ability- Flat predicting the future is a no-go as far as a y1 natural ability goes and even fully grown it would severely downplayed. I honestly would avoid this until she's older and more mature, though anything that has to do with predicting the future will need approval. A better year 1 natural ability for a naiad might be that she can 'melt' into bodies of fresh water bigger than puddle. She can use this to move around provided the locations are connected by the fresh water. (I say freshwater as that is type of water Naiad's come from).

Personality is rather intorverted and aside from being shy and quiet there is not much for her personality. Is she kind, selfish, needy, vain, thoughtful- examine her inner workings rather than outer!
I'm also going to crit on this chunk:
'She blames her beautiful looks for this problem. Thalassa just can't get a break She believes that her beauty is a drawback. Instead of being left alone she is being hounded by ghouls trying to get with her. She has girls wanting to come up to her and fight her cause their man looked at her. She gets mistaken for either a model. The cheerleaders want to hang out with her inviting her to go shopping or to sleepovers. She tries to make herself unattactive in order to avoid unwanted attention but nothing she does seems to work for her. '
You're predetermining things such as other players views of her, actions towards her, and go on about how beautiful she is. Please do consider rewriting this as you can't control how players will view your girl or how they will act around her. Try to remove anything that talks about how other players/characters will view her, (girls wanting her, mistaken for a model, the cheedleaders wanting to be around her, girls wanting to fight her, ect). You can mention how she THINKS of herself as beautiful and that she things it draws to much attention to herself but determining other character's views is a huge turn off for RPing.

Reason to enroll is good, FEAR attack has me going??? because do you mean a whirlpool of water and if so, why above vrs below? It would make more sense to me if she made a small whirlpool below or around them.
Pick from the FEAR guild what your FEAR does too! (battle cry, mind, barrier, ect) Just so we know~

done.

Thank you for your help. heart
I will get on the changes when I come back from school.