A revamped vault of glass with atheon and the rest brought back by the SIVA virus
Edit:1 Lore wise could be difficult but Rasputin controls the SIVA from my understanding so let's say either a fallen kell tries what skolas does but the SIVA infects the vex or maybe the vex launch an attack on the fallen or Rasputin and are infected that way all I'm saying is its possible at least
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That would be a really good plot twist of vex spliced themselves with SIVA. Imagine how rapidly the virus would spread, no way we could control. Vex raid in the winter/ spring?!?! Idk pulling stuff from my butt here