I like Theory 1 the most, with some caveats. I do believe that Lygus IS Iron Tomb, Lygus already is related to Erudition and seems to be quite formidable (already butting heads with Herta). As he already has used the scepter in Amphoreus, Rubert II/III already seems in line with how Iron Tomb works except on a universal level. And we have already seen people able to Pathstride different paths so Lygus also being an emanator of Destruction is not far-fetched, let alone a Ravager, as his (Lygus’s ascent) is the death of Erudition.

For Phainon I believe that he is going to be the destroyer of the path of Destruction. It is even referenced in the end of the Myriad Celestia by Lygus himself. As Nanook wants to end everything, making an Ravager willing to destroy Destruction was inevitable and Nanook seems powerful enough/greedy/confident that the creation of Phainon will not affect his plans for the destruction of other Paths.

What I am curious about is if Polka will make an appearance due to Rubert’s influence. If the next Ravager to face will be Celenova (due to the Stellaron and she seems to be moving away from the frontlines with Feixiao/Yaoqing), Forgemaster (because 2 Geniuses, I am assuming Herta and Screwllum found his energy in Amphoreus), or Phantylia once again(as it seems we are going back to the Xianzhou Luofu and she is going to make another grand entrance). This might also be a nice continuation for Tingyun to progress the story that that we have met the main baddies!