I remember reading about it here. The developer demoed an especially difficult fight, in which tons of demonic monsters kept spawning and he kept dying and having to start over. He said the whole game was hard like that, and the writer of the article seemed enthusiastic about that.
It had a dark kind of Diablo-like isometric perspective aesthetic, with stone columns and walls, and I think iron bar walls and doors. There may have been braziers with fire.
This could have been any time from last year to three years ago. I have no sense of time.
Any idea what it could have been? I’m having no luck with searches.