If Percy Jackson goes to Valhalla in fanfiction, he could meet a whole bunch of Norse heroes. There's Sigurd, the dragon - slayer. And then there are the Valkyries who choose who gets to go to Valhalla. He might also run into Loki, who is always causing some sort of trouble. Percy would be in for quite an adventure as he tries to figure out who he can trust among these new and often unpredictable characters.
In this fanfiction scenario where Percy Jackson goes to Valhalla, he'd surely meet the Einherjar, the dead warriors who fight and feast in Valhalla. These warriors have their own stories and skills. Percy would also likely cross paths with Freya, the Norse goddess of love and beauty. Their encounter could be really interesting as Percy comes from a different mythological background and might have a different view on things compared to the Norse characters.
Percy might run into Loki. Loki is known for his trickery. He could either befriend Percy for his own devious plans or try to deceive him. Percy, being used to dealing with tricky situations in his own world, would have to be on his guard against Loki's schemes.
He would probably meet Eragon. Eragon is a key figure in Alagaesia, and their encounter would be full of surprises as they come from different worlds with different powers.
Well, he might meet some really tough Norse warriors. Maybe he'd get into some epic battles or challenges. He could also make new friends or enemies among the Norse gods and heroes there.
He might first meet a human. Azeroth has a lot of human settlements, and it's likely that Percy would stumble upon a human village or town first. The humans would be both curious and cautious about him, especially if they notice his strange powers.
There's also a chance that he'd meet Lydia first. Lydia has her banshee powers, and she might be drawn to Percy because of his otherworldly presence. She could sense something about him that's not of this world, and approach him out of curiosity. Their meeting could be a very intense and mysterious one, with Lydia trying to figure out what exactly Percy is.
He might meet a new teacher who is secretly a minor god or goddess in disguise.
Percy might meet an old enemy who has somehow been resurrected or changed in the future. This enemy could be more powerful and have a new plan to take over the world or destroy the demigods. Or he could meet a group of time - traveling demigods from an even further future who are trying to fix something in Percy's future that has gone wrong.
He could meet some Aboriginal heroes or spirits. They might have their own powers and knowledge that Percy can learn from.
He might meet Luke before he turned bad. Percy could try to change Luke's fate, convince him not to follow Kronos. It would be a great chance to save a friend and prevent a lot of the chaos that happened later.
He could meet other demigods from different pantheons. Since it's a different world, there might be demigods associated with gods that Percy has never heard of before.