Dude thank you so much for playing and making a video! It means a ton to the team, we are all giddy with excitement. To activate a legendary run you must speak to the informant inside the thieves guild (guy to the left of the initial spawn on a new game). You will get a riddle that involves you finding and using certain items. Good Luck! We are going to work on making that more apparent in the future.
And thank you for making and posting the game. It's a fun play so far. I did eventually find the informant purely by chance after that video, though his riddle didn't help me much.(Not that I won't keep trying.) I also managed to find a bug. There's a cellar behind one of the houses and trying to open it causes it to flip upright like a normal door and renders the cellar inescapable.