Regeneration potion

"Bone of the father, unknowingly given, you will renew your son! Flesh of the servant, willingly sacrificed, you will revive your master. Blood of the enemy, forcibly taken, you will resurrect your foe."

- Peter Pettigrew reciting the incantation for the potion's creation.

The Regeneration potion is a Dark potion that restores a wizard whose body has become maimed and disfigured to their true and whole bodily form.

Overview
The potion requires a cauldron large enough for a grown man to sit in as well as three crucial ingredients: bone unknowingly taken from the Dark Wizard's father, flesh willingly sacrificed from one of his servants, and the blood forcibly extracted from one of his foes. The remainder of the ingredients, if any besides water are needed, remain unknown.

Past
"- it is an old piece of dark magic, the potion that revived me tonight -"

- Lord Voldemort's description of the Regeneration Potion

As Voldemort noted the potion to be "an old piece of dark magic", it can be inferred that it has been used in the past by other Dark Wizards who suffered bodily damage. Therefore, Voldemort most likely did not invent it.

Voldemort's rebirth
"The Dark Lord shall rise again!"

- Wormtail as he completed the potion to restore his Master in 1995.

In 1994, Lord Voldemort had Wormtail prepare the potion, save for its most crucial ingredients, for his rebirth. While Voldemort had the flesh at hand due to Wormtail's presence and could easily gain access to his father's bone from his grave, he wanted Harry Potter's blood to rise "greater and more terrible" than before his fall. Through a complex plan, one of Voldemort's loyal servants, Barty Crouch Jr., managed to send Harry to him. With the three ingredients, Voldemort's rudimentary form was included into the cauldron, and he was able to regain his new body.

The use of Harry's blood in the potion, however, would come to be a mistake as it prevented Voldemort from killing Harry because the blood passed Lily Potter's protection to Voldemort and anchored Harry to the living world through him, ensuring the Dark Lord's defeat three years later. Voldemort believed, out of his lack of understanding love, that by using Harry's blood, it would allow him to bypass Lily's protection, when in fact it actually strengthened it.

Behind the scenes

 * In LEGO Harry Potter: Years 1-4, Peter Pettigrew used Harry's glasses and Riddle's cranial bone, most likely to avoid violence. Instead of using a knife, Peter Pettigrew simply takes his hand off. When Voldemort is returning he wears Harry's glasses. Also, Voldemort is sucking a dummy as a baby and lies in a pram. Also, Voldemort rises from the cauldron, but already has his cloak on.
 * In the novel, the bone was no more than a trickle of dust raised from Riddle's grave, and Voldemort rises from the cauldron while ordering Wormtail to cloak him. In the film, an entire bone that was already dug up was deposited into the cauldron, which catches fire and melts as Voldemort's body regenerates in mid-air and the cauldron's fragments gets Transfigured into a cloak.

Appearances

 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Goblet of Fire (film)
 * Harry Potter and the Deathly Hallows
 * LEGO Harry Potter: Years 1-4