Nura is definitely one of the strongest heroes... her ability to restore mana during battle is amazing... Around level 15, you can cast spells as much as you want... the main thing is that your troops hold out. You can take Light and Darkness... Divine Retribution will mess with the enemy troops, and Darkness will give you Berserk and Subjugation, and they will destroy themselves... and you can poison Elves with Plague... weakening the troops of Demons and Necromancers - they won't even want to fight anymore... Chaos and Summoning are also good options... Phantoms, Shields, Walls of Fire... and with Chaos, you can just keep attacking - it's a lot of fun... As for the other skills, you definitely need to take Spellpower.

Added 5 minutes later
And what is with all this talk about Oracle? Her ability doesn't give any effects... except that she moves earlier than other heroes... and the casting frequency increases by a negligible amount... some fractions of a percent... Nura also has Magic Arrow at the very beginning, and her mana runs out slowly... as a result, you can level up the hero faster than others and capture mines... well, I don't know, Nura has always led me to victory... And one more fact - she is a Djinn and is already unique in her own way.