I ran through various forums, no one knows)
Solid - "Rostan Muggs is back" So who/what is Rostan Muggs. And where to find him/her/it ?
I found him, standing not far from the southern gates of Novigrad towards the tavern Seven boilers, he has a square
So since he came back, that must have meant something? Who is he? Something I don't remember such a character in the previous 2 parts of the game...
No, I don't remember him in the books either, although the name is memorable. Maybe it's from Storm Season? I haven't read it yet.
My suggestion.
Perhaps there was a bug in the game due to which this NPC disappeared or was removed, and in patch 1.03 the developers returned this character. And in the changes to the patch they wrote that he was back. Just like a remote NPC.
It's just a hunch.
As far as I remember, the appearance of the down player was copied into the game and it is unique - there are no other NPCs with such an appearance.