And you can upgrade magic in only one way, although I won't say how (it's a trade secret).
Once again: I'm playing HotS, so my opponents will notice what I'm doing, and to put it mildly, I'm doomed. :)
A staff isn't bad, but why the rest of the junk from the set?
1) -2 to enemy morale and luck
2) -20% initiative
3) -1 speed!!!! - that's what's important against an Elf!!!
but I think Nimue is still better here, because we need more gating to kill more strong, lucky Elves at once.
The enemy will have a tactic, and probably Retribution. And they might not even have True Sight.
Therefore, so that the opponent doesn't use tactics, we'll take Nebiros, because with Nimue, troops will be summoned and sometimes, without a turn, except for the horses and dogs summoned, they will retreat back to hell.
The problem with Nebiros is that you'll have to change his tactics to something to achieve Super Units, and his special ability is weak...
But the choice is bad, because Inferno doesn't have any particularly strong counter-heroes against Elves...
You can try, but only not in an open field. Nimue is best for sieges or defending a castle... But how do you lure an Elf there?
Of course, you can try to upgrade Nimue with Light spells, Storm spells, and find spells + cloak + staff + ring of speed. But the Elf will have tactics, Boots of Striding, aura of speed... It's tough... here you can only rely on good luck and the opponent making a mistake. If only Super Units were acquired on the way to achieving Super Units...