Thor could also be a candidate in some fanfictions. Given his god - like status and connection to powerful Asgardian magic, he could be fated to become the 'Master of Death'. It would be a huge transformation for his character, from a warrior god to a being with the power over life and death.
One possibility could be Doctor Strange. With his vast knowledge of the mystic arts, he might stumble upon the power of the 'Master of Death'. His already existing powers over magic and the multiverse could be a stepping stone to this even greater power.
It could be an ancient shinobi who has mastered some kind of death - related jutsu and has ascended to a higher state of being. This shinobi might have been forgotten in the history of the ninja world.
It could work if the Infinity Stones and the Deathly Hallows had some sort of connection. Since Harry is the Master of Death, he might be sensitive to the power of the Stones. The Avengers are dealing with the Stones' power, and Harry could bring his knowledge of dealing with powerful magical artifacts from his world. He could teach the Avengers about the consequences of misusing powerful items and how to safeguard against the corrupting influence of such power.
Another possibility is that Death is being controlled or influenced by a greater cosmic entity. In this case, that entity could be the main antagonist. It uses Death as a tool to test or destroy the Avengers. The Avengers would then have to not only deal with Death but also find a way to face this more powerful and mysterious entity behind Death's actions.
Well, the portrayal of the 'Master of Death' can vary a great deal. Sometimes, it's a character who has acquired this title through some dark magic or ancient artifact. They are then feared by many in the Avengers universe. In other cases, it could be a hero who reluctantly takes on this power to stop a greater evil. This can create a lot of internal conflict as they struggle with the implications of having such god - like abilities.
Nico di Angelo has a strong connection to the Underworld, so he's a prime candidate. He can already communicate with the dead and has some control over the shadows, which are related to death in a way. In fanfiction, he could be further developed to become the Master of Death, perhaps by making a deal with Hades or finding a hidden power within himself.
Perhaps it could be a character like Bran Stark. He has the power of the Three - Eyed Raven, which gives him access to a vast amount of knowledge and some control over time and events. It's not a far stretch to think that he could develop into a Master of Death in a fanfiction.
One possibility could be that Harry uses his mastery over death to bring back some fallen Avengers. He might use his knowledge of powerful magic to enhance the Avengers' abilities. For example, he could place protective spells on them similar to the ones used in Hogwarts.
A new character created specifically for the fanfiction could also be the Master of Death. This character could be a hybrid of a wizard and a vampire or werewolf, having the combined knowledge and abilities of both worlds. They could use their power to try and create a new order where wizards, vampires, and werewolves co - exist peacefully, using their mastery over death to enforce certain rules.
It could be an epic crossover. Harry, with his mastery over death, might bring some unique magic to the Avengers. Maybe he could use his skills to revive fallen heroes or protect the world in a different way than the Avengers are used to.
The three Avengers could be Iron Man, Captain America and Thor. Iron Man could provide the high - tech gadgets and strategic thinking. Captain America would bring leadership and his combat skills. Thor with his godly powers like lightning and super strength would be a great addition. They would each have different interactions with Spiderman, for example, Iron Man might be like a mentor to him, while Thor could be more of a friendly rival in terms of strength.