>>45823097>She is stronger than Arceus canonically as she came before him.>FanfictionAs per OP's question, it has similarities to Ultra Beast, a design/theme very reminiscent of them. Could have been called UB:Eternal and the lore could've been the exact same.
As for creature basis, quite obviously an "undead" or corrupted dragon. Kinda reminds me of the Archdemons from the Dragon Age series, if only the comparison weren't an insult to Bioware. The Eternamax also reminds me of a Reaper, who along with the prior mentioned Archdemon dragons have Lovecraftian basis. Tbf that first poster is correct about the Eldritch horror part, but it was never mentioned that it's a "god of chaos predating Arceus" anywhere in canon.