I just checked and yes, it's the flux one, plus a couple others that sound like optional boss fights. They don't seem overly difficult, perhaps I just moved on to another game at the time.
Sander Rossel wrote:
Still playing Hades?
No, I haven't played it for a while. I may go back to it, not sure yet. I ungraded to PS Premium (or whatever the top-tier one is called), so I have been played a bunch of random games that are available on that. Including getting the platinum for Wild Arms :)