One possible plot could be that the Ashen One from Dark Souls is transported to the Marvel Universe. They might be mistaken for a new superhuman or a threat. The Ashen One's skills in combat and their ability to endure great hardships could make them a formidable force. They could team up with the Avengers, perhaps initially clashing due to misunderstandings but then realizing they share the common goal of protecting the world from greater threats like Thanos or other powerful villains. The Ashen One could teach the Marvel heroes about the concept of 'kindling' or 'linking the fire' which could be metaphorically related to the heroes' own struggle to protect their world and its various sources of power.
The X-Men are part of the Marvel Comics lineup. They have their own unique place within the Marvel multiverse, with a dedicated fan base and a significant impact on the comic book world.
The Chosen Undead from Dark Souls could be seen as a mutant in the Marvel Universe with their ability to keep coming back to life. They might be shunned at first like many mutants are, but then prove their worth when facing threats. Their combat skills with swords and shields would be a unique addition to the fight scenes in the Marvel Universe. For example, they could fight alongside Wolverine, and their different fighting styles would create an interesting contrast.