'Goblet of Fire' and onwards are now non-canon; Horcruxes and the Unforgivable Curses are no longer a thing. What is Voldemort's modus operandi and magic of choice, and what is the secret to his immortality?

Harry Potter books before Goblet of Fire: The magic Voldemort uses is a mystery, nobody knows how he survived death and returned as a wraith, his followers could be anyone.
Harry Potter books after Goblet of Fire: This is the visual indicator that someone is a follower of Voldemort. This is a list of Voldemort's favourite spells, and the only ones he knows in bashing fanfics. This is how he survived his death and how to kill him properly.
 
If all of the mainstays of fanfic introduced in Goblet of Fire (Apparation, Portkeys, kitchens full of house-elves, the Dark Mark, Unforgivables) didn't exist, and the Horcruxes weren't introduced in Half-Blood Prince...what would you do with Voldemort?
What would you make his magic and tactics of choice? Would he be the straight-up deadliest duelist in the world, or would he be a possessor leaping from body to body and using countless innocents as human shields?
What of his immortality? Did he follow in the path of Koshchei the Deathless, imprisoning his death (or Death) in a receptacle so it could not claim him? Is he an invader from some lower realm, returning again and again until the gate to the underworld is shut?