Well, perhaps Harry stumbles upon a unicorn in the Forbidden Forest that is trapped by some dark magic spell. He uses his magic skills, like a Patronus charm to fend off the dark forces around the unicorn and then heals it with some herbology knowledge.
It could be a rogue Death Eater who has escaped from Azkaban. This Death Eater might be desperate to regain his power and believes that unicorn blood will give him the strength he needs. So he sets out to capture a unicorn in the Forbidden Forest, which is where Harry comes in to stop him.
In a 'Harry Potter blessed by a unicorn' fanfiction, the plot could center around how the unicorn's blessing affects Harry's relationships. For instance, it could make him more attuned to the emotions of his friends. He might be able to sense when they are in danger or distress even from a distance. This could lead to new adventures where he has to save his friends using the powers bestowed upon him by the unicorn. Also, the other magical creatures in the wizarding world may start to view Harry in a different light, seeing him as a chosen one in a new sense, which could either attract allies or create new enemies.
In such a fanfiction, perhaps Harry uses his magic skills learned at Hogwarts. He might first find the injured unicorn in the Forbidden Forest. Then, using a spell like 'Episkey' or some advanced healing magic he's discovered. The unicorn could be injured by dark creatures or a trap set by poachers.
In this fanfiction, perhaps the centaur is in a situation where it's about to be sacrificed in some dark ritual. Harry discovers this and races against time to stop it. He calls upon his friends Hermione and Ron for help. Hermione uses her vast knowledge of magic to figure out how to break the dark magic circle, while Ron provides some much - needed comic relief during the tense situation. Harry, of course, is the one who ultimately uses his powerful Patronus charm to dispel the dark forces and save the centaur.
Well, perhaps Zoe is in danger from dark wizards. Harry, with his skills and bravery, could use spells like Expelliarmus to disarm the villains threatening Zoe. He might also use his invisibility cloak to sneak up on them.
The fanfiction could show that Harry discovers a secret passage that leads to where Cedric is held captive. He has to face various magical traps and challenges on the way. Once he reaches Cedric, he uses his Gryffindor courage and his knowledge of magic, like the Shield Charm to protect Cedric from incoming spells, and then they escape together, with Harry being the hero who saves Cedric.
One possible plot could be that Harry, through some magical accident or powerful spell, is transported to the world of Cintra. There, he discovers the danger it's in. Using his magical skills like the Patronus charm to ward off dark creatures threatening Cintra, and his knowledge of spells to help in battles. He might also form alliances with the local warriors, teaching them some basic magic for self - defense.
In a 'Harry Potter Saves Bellatrix' fanfiction, perhaps Bellatrix is in a situation where she's about to be killed by other Death Eaters who think she's a liability. Harry, having a sense of justice and seeing the potential for redemption in her, steps in to save her. He could then try to show her the error of her ways, using his own experiences of losing loved ones to Voldemort's ideology. Bellatrix might initially resist, but gradually come to understand Harry's point of view.
Well, perhaps the vampire is being hunted by some dark wizards. Harry Potter, being the hero he is, uses his magic skills like the Patronus charm to fend off the attackers and save the vampire. Maybe the vampire has some crucial information about Voldemort that Harry needs.
Maybe Harry uses his magic skills like the Patronus charm to protect the Jedi from the Sith. His ability to apparate could also help Jedi in quick escapes.