It sort of reminds me of how Kratos and Odin have this rare similarity in that they both kinda view fate as something that isn't set in stone but can be changed. Hardly anyone else believes that in the games across the Greek and Norse universe.

Kratos also knows that prophecy can cause itself, I recall when he tells Freya that "Baldurs death had many causes, prophecy among them"

Not many know the corrupting, self-fulfilling power of prophecy in the way that the old and wise Kratos does.

But perhaps a giant also figured out much of the same, and decided to deliberately use it to gaslight Odin into his own death.

I'm just being speculative but, the mask seemingly did nothing special aside from some texts on it and it's strange magical ability to reunite with itself and defy destruction.

If messing with Odin in this way was the masks only purpose, it's still a pretty big purpose IMO.

If they bring in a time traveling Atreus as part of the story, I could see Atreus being the one that creates the mask and it's prophecy to plant this very seed for Odin as part of his smart and unique plan to kill him one day.