Dwarf -> Dwarves
Smurf -> Smurves
Olympix -> Olympices
(but this doesn't apply to Mt. Si, which is a Cascade, or Mt. Washington which is an Appalachian)
@mcnees @Lazarou Better example needed. As Tolkien said, “dwarves” was an error.
“No reviewer (that I have seen), although all have carefully used the correct dwarfs themselves, has commented on the fact (which I only became conscious of through reviews) that I use throughout the ‘incorrect’ plural dwarves. I am afraid it is just a piece of private bad grammar, rather shocking in a philologist; but I shall have to go on with it.”
Not that it matters of course. Language is what we make it. So with luck (and an amazingly popular book) you may be able to make smurves cannon. :)
https://jakubmarian.com/dwarves-or-dwarfs-which-spelling-is-correct/