Rudimentary body potion

"It was as though Wormtail had flipped over a stone, and revealed something ugly, slimy and blind — but worse, a hundred times worse. The thing Wormtail had been carrying had the shape of a crouched human child, except that Harry had never seen anything less like a child. It was hairless and scaly-looking, a dark, raw, reddish black. Its arms and legs were thin and feeble, and its face — no child alive ever had a face like that — was flat and snake-like, with gleaming red eyes. The thing seemed almost helpless..."

- Harry Potter describing Voldemort's rudimentary body.

The rudimentary body potion is a potion likely invented by Lord Voldemort. It was prepared for him by Wormtail and was used to create Voldemort's rudimentary body in order to sustain him while he awaited his return to power. Two of its main ingredients were unicorn blood and Nagini's snake venom. The drinker must continuously drink the potion every few hours in order to maintain the little health that they have regained.

History
The potion and its associated rituals were able to create a rudimentary body for Lord Voldemort's disembodied soul-fragment to be directly transferred into. The body was small, about the size of an average baby, and shriveled, but still retained some of Lord Voldemort's true body's distinctive characteristics, such as his snake-like nostrils and red, slitted eyes. This body's physical abilities were extremely limited and while in this form, Voldemort needed Wormtail to transport him from place to place and tend to him constantly. His magical powers were also greatly reduced in this small and a bit vulnerable state, although he was still powerful enough to cast an effective Killing Curse as well as turn Nagini into a Horcrux at some point.

This body was used until Voldemort, with the aid of Peter Pettigrew and Barty Crouch Jr., was able to create the ancient Regeneration Potion to finally restore him to his true body and abilities. Prior to that, the body that the potion provided Voldemort was so gruesome, it revolted both Frank Bryce and Harry Potter greatly, and caused Pettigrew to flinch when seeing it, and shudder when holding it.

Behind the scenes

 * It is unknown how Voldemort managed to take this potion before acquiring his temporary body, as he was still in a mangled spectral state before the first time being fed the potion. This was a similar case in how the ghost Nearly Headless Nick partook the Mandrake Restorative Draught. However, given Voldemort's power of possession, he may have been occupying the body of someone or something in order to take the potion.
 * In the book Harry describes Voldemort as blind. But in the movie he ask Barty Crouch Jr. to see the Dark Mark on his arm.
 * The deformed body that Voldemort inhabited through this potion resembles his mangled soul when Harry was in Limbo.

Appearances

 * Harry Potter and the Philosopher's Stone (film)
 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Goblet of Fire (film)
 * LEGO Harry Potter: Years 1-4