Thor could be one. Maybe he thinks the dragon egg is too dangerous in Loki's hands and wants to take it away for the safety of the realm. Or Odin, who always wants to control powerful artifacts. He might see the dragon egg as something that should be in his possession.
Perhaps Loki first thinks about using the dragon egg as a bargaining chip. He could approach other powerful beings in the fanfiction world and offer the egg in exchange for something he desires, like more power or a way to get back at his enemies. But then he might change his mind when he realizes the dragon's potential loyalty to him.
There could be a really interesting fanfiction where Loki, being his mischievous self, stumbles upon a vault in a dragon - guarded kingdom ruled by a powerful queen. Maybe he's initially after some powerful artifact in the vault for his own gain, but then gets caught by the dragon. The queen then has to decide what to do with him, and in the process, they all learn something about each other and their different worlds.
Daenerys Targaryen could be one to help. Since she has experience with dragons, she could give Jon Snow advice on how to care for the egg and hatch it.
Hermione would most likely help. She's always been there for Harry, and with her vast knowledge from books, she could offer a great deal of advice on how to take care of the dragon egg. Ron might also be involved. Despite his initial fear of things, he has a brave heart and would probably stand by Harry's side.
It could be a dark wizard or sorcerer who wants the dragon egg for its power. They might try to steal the egg from Bella.
He might meet an old Pokémon expert who gives him tips on hatching the egg.
In this fanfiction, the vault might be a prison for an ancient evil. The queen has the key, and the dragon is the guardian. Loki, thinking he can control the evil, tries to steal the key from the queen. But the queen has her own magic and the dragon its strength. As Loki tries to scheme his way in, he gets caught up in the queen's plans to finally destroy the evil. Along the way, Loki might change his mind about his motives, and they all fight together against the real threat that lies within the vault.
Team Rocket would be the most obvious ones. They're always after rare and powerful Pokémon or Pokémon - related items, so the legendary egg would be a huge target for them.
His best friends Hermione and Ron would surely be there to help. Hermione with her vast knowledge of magic could research about the egg, and Ron with his loyalty would stand by Harry's side in any danger related to the egg.
Maybe Kakashi. He's very experienced and wise. He could share some of his knowledge about strange things he has encountered before. He might help Naruto understand the significance of the egg and guide him on what to do with it, whether it's to keep it safe or to find its rightful place.