Well, in this kind of fanfiction, the relationship between Jack Frost and the original character (OC) can be really diverse. It could be a friendship where they start off as strangers and gradually become close pals, perhaps sharing their unique powers and experiences. For example, the OC might have a special power related to nature, and they team up with Jack Frost to protect the world from some dark force.
A good one often has well - developed characters. For Jack Frost, his transition from his normal form to human (if that's the plot) should be believable. The writer should capture his essence, like his mischievousness and his connection to winter. Also, the story should have a solid plot. Maybe it's about Jack Frost experiencing human emotions for the first time and how he copes with them. Good grammar and spelling are also important as they make the reading experience smooth.
Another plotline could be the OC being in danger, and Jack Frost having to rescue them. This could be because the OC has a special power that some evil force wants to steal or because the OC has accidentally stumbled into a dangerous situation while exploring the magical world. Jack Frost then uses his ice powers and his wits to save the OC and keep them safe.
One possible plot could be that Jack Frost is corrupted by a dark force. He starts to spread winter not as a fun, playful season but as a harsh, unforgiving one. He might turn against the other Guardians, believing they are holding him back from his true power.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). There are often a lot of filters you can use to narrow down the search specifically for Jack Frost human fanfiction in the 'Rise of the Guardians' fandom. Another option is FanFiction.net, which has a large collection as well. Some Tumblr blogs also curate and share great fanfiction, so searching relevant tags there might be fruitful.
Pitch Black would be a likely main antagonist. He could manipulate Jack Frost into turning dark, as he has a history of preying on the insecurities of the Guardians.
The main characters are obviously Jack Frost and the Guardians. The Guardians typically include characters like North (Santa Claus), Tooth (the Tooth Fairy), Bunny (the Easter Bunny), and Sandy (the Sandman).
He might not be able to spread as much joy. If Jack is hurt, his powers could be weakened. So, the children in his area may start to feel less happy and more afraid, as his presence and ability to create positive wintery magic is reduced.
In many fanfictions, Jack could get hurt in a fight with Pitch. Pitch might use his dark sand to create dangerous illusions that Jack stumbles into, resulting in physical harm like cuts or bruises.
One great 'rise of the guardians jack hurt' fanfiction is 'Frost's Trial'. It delves deep into a situation where Jack gets physically hurt during a battle with a new, powerful dark force. The author does an amazing job of showing his struggle to recover and how the other guardians react.