He uses his combat skills. Percy is a skilled fighter, so he'll likely rely on his sword - fighting abilities to take on the monsters he encounters in Tartarus.
Percy, in the fanfic, would use his wits. He has always been clever, and in Tartarus alone, he'd have to figure out ways to avoid traps and overcome obstacles. He might also try to communicate with the environment, since he has a connection to water and Tartarus surely has some form of liquid element that he could potentially manipulate. He would have to be very careful though, as one wrong move could mean his doom. Another way he could deal with the challenges is by making use of any remnants of his godly heritage that he hasn't fully explored yet. This could give him an edge in the otherwise hopeless situation.
He uses his wits. Percy has always been clever, and in Tartarus, he'd use that to his advantage. He'd find ways to outsmart the monsters, like using the environment against them.
He might use his sword skills and his ability to control water. For example, he could create shields out of water to protect himself from attacks. He would also try to find any weaknesses in his enemies. If there are any water sources in Tartarus, he could use them to his advantage, like making geysers to distract or attack his foes.
Well, one possible plot could be Percy facing his inner demons in Tartarus. Since he's alone, he might have to rely solely on his own skills and memories. Maybe he'll encounter some long - forgotten monsters that test his strength and willpower. He could also stumble upon some hidden secrets about the place that no one has ever known before.
It could be Nyx. She is a very powerful primordial goddess in Tartarus. Since Percy is alone, she might see him as an easy target or a threat to her domain. Nyx could send all sorts of dark creatures and illusions to stop Percy from achieving whatever goal he has in Tartarus.
In some fanfictions, Percy uses his sense of humor as a coping mechanism. He might make light - hearted jokes about the Tartarus situations in the nightmare to Annabeth when they wake up. Annabeth, on the other hand, might try to analyze the nightmares. She'd break down the elements and figure out what in their subconscious is causing these dreams.
Well, one possibility could be Percy facing his inner demons. In Tartarus alone, he might have to deal with the memories of his past failures and the fear that comes with being in such a desolate place. He could encounter strange and terrifying creatures that test his combat skills and his will to survive.
One popular Percy Tartarus Alone fanfic could be 'Surviving Tartarus: Percy's Solitary Struggle'. It might focus on Percy's inner strength as he faces the terrors of Tartarus alone. Another could be 'Percy in the Depths of Tartarus', which may explore how he uses his skills and wits to overcome the various challenges.
He might face numerous terrifying monsters. Tartarus is full of dangerous creatures in the fanfic world, and Percy would have to fight for his survival all by himself.
There's a chance that Percy meets the personification of Tartarus itself. It could be a shadowy, all - powerful being that tries to break Percy's spirit. Percy, being the brave hero he is, would have to resist and find a way to either outwit or overpower this entity in order to continue his journey in Tartarus.
Perhaps Percy has to go to Tartarus alone because he believes it's the only way to save his friends. In Tartarus, he might encounter old foes who are now even more powerful. He has to rely on his wits and his skills with his sword, Riptide. He could also make unexpected alliances with some of the creatures there in order to survive and achieve his goal.