You could make him REALLY big and also unkillable unless you’re holding a Silmaril and are in a boat (because that’s how he dies in the book, albeit, more dramatic). And if you kill him in this way, he could drop a component for the light of Earëndil.
And this would also mean that there would need to be Silmarili (plural of Silmaril) they could be like REALLY rare drops from Utümno tortured elves. (A reference to Melkor killing Fëanor’s father and taking the Silmaril back to Angband by force).
Then you could combine a Silmaril with the component dropped be Ancalagon and craft the Light of Earëndil.
I know that the mod is mostly Third age. And that all the events above took place in the years of the trees and the first age. (Specifically the war of Wrath). But I think it’d be pretty cool.
And the achievement for doing all this could be called: “The voyage of Earëndil”. And there could be a shield as a reward, maybe a scale from the dragon.
As for what the light of Earëndil would do… I honestly don’t really know… I’ll leave that up to you.

