give me more data to feed to the machine god, it's actually pretty good at this but it takes a couple back and fourths like
https://en.akinator.com/ did back in the day
While none of the search results directly describe the exact sequence of events you mentioned (battle outside a tomb with a killer fog or smoke), Berserk aligns with the broader themes of demonic battles and potentially confusing scenes from other dark fantasy anime.
To get a more precise answer, can you remember any additional details, such as:
Character names?
Any specific visual elements of the fog or smoke?
The appearance of the demon king?
The general aesthetic of the anime?
More information may help identify a specific anime or scene that matches your description.