According to Dumbledore, when Tom Riddle left Hogwarts he disappeared, traveled, and “sank so deeply into the Dart Arts…underwent so many dangerous, magical transformations, that when he resurfaced as Lord Voldemort, he was barely recognizable.” (CoS) Assuming most of his attempts to cheat death happened during this time period, our best clues to what he did may be found in his appearance.
The face under the turban in SS/PS: “chalk white with glaring red eyes and slits for nostrils, like a snake.”
As Harry described him popping out of the cauldron in GoF: “Whiter than a skull, with wide, livid scarlet eyes and a nose that was flat as a snake’s with slits for nostrils…His hands were like large, pale spiders; his long white fingers…the red eyes, whose pupils were slits, like a cat’s” – and later: “unnaturally long fingered hands” and “lipless mouth”
Just in case we missed that, the finer points are reiterated in OotP when, in the infamous Rockwood Dream, Harry looks in the mirror before returning to himself: “A face whiter than a skull…red eyes with slits for pupils…”
And again when he arrives at the MoM: “Tall, thin, and black-hooded, his terrible snakelike face white and gaunt, his scarlet, slit-pupiled eyes staring.”
One of his many references to his voice in the PoA series of memories specifically mentions “a cackle of high-pitched laughter” (240, PoA)
Now compare that to these descriptions:
“Harry had never met a vampire, but he had seen pictures of them in his Defense Against the Dark Arts classes, and Black, with his waxy white skin, looked just like one.” (38, PoA; also, keep in mind on p. 17 he also described him as pale and “gaunt”)
“the eyes of the black dragon, with vertical pupils like a cat’s” (GoF) – The Hungarian Horntail Harry fought had yellow eyes but…
“The scales are metallic grey, the eyes deep red, and the talons particularly long and vicious.” – Ukrainian Ironbelly, the largest breed of dragon. (FB)
“a high-pitched cackle” the Erkling (FB). This 4X beast (compared to the dragon’s 5Xes) is known to attack children. Interestingly, in the last known Erkling attack, this dangerous beast was killed by the very child it attacked.
Perhaps the unicorn blood and snake venom is just the tip of the iceberg. Perhaps, in his quest for immortality and power, he’s concocted potions from and performed transformations with the strongest and most dangerous magical creatures he could find in an attempt to transfer their strengths to himself. What could be harder to kill than a vampire, a dragon, a unicorn, an Erkling, and a basilisk all morphed into one? (Note: if anyone stumbles across a mention of something described as “whiter than bone” or “chalk white” I’d really like to hear about it.)
This brings a new twist to Hagrid’s statement, “I don’t reckon there was enough human left in him to die,” (SS/PS) and Harry’s “THEN I DON’T WANT TO BE HUMAN!” (OotP) which, as another editorial has already pointed out, may have been the Voldemort-Connection talking. Consider this little GoF statement by Voldemort: “But I am not a man, Muggle. I am much, much more than a man.” (15)
Why, then, would his soul stick around when his body finally was destroyed? Simple, the phoenix – a creature one simply couldn’t overlook when searching for animal resources for cheating death. This mystical bird’s unique ability to regenerate itself comes in two parts. First, the soul doesn’t go anywhere. It stays close, ready to re-enter the new body, apparently within seconds. Second, there is a new body. From the ashes of the old, a new body automatically regenerates itself instantaneously.
Voldemort’s GoF comments regarding his resurrection are telling: “it appeared that one or more of my experiments had worked…for I had not been killed…” He seems surprised. And why shouldn’t he be? These are not the sort of experiments one tests to be sure they’re working. This is JKR’s way of reminding us that all this is still highly experimental magic. Even if he is among the greatest wizards of the age (though certainly not #1), there’s no guarantee that any of this worked. I believe she’s setting us up for a major revelation later on: the Phoenix Transformation only partially took. While VaporMort stayed behind like a good little essence, it seems the spell failed to recreate the automatically regenerating body the birds are known for – leaving VaporMort essentially homeless.