He tried using "Avada Kedavra" 6 times, but one time he could not completely utter the curse.
But it's the “Avada Kedavra” killing curse, one of the three Unforgivable spells in the Potterverse, that really catches our attention. It holds a concerning sixth place on the list with a total of 21 uses throughout all seven books.
Throughout the Harry Potter movies, Voldemort used the Killing Curse on several characters, including Alastor Moody, as well as Lily and James Potter. However, he didn't always use Avada Kedavra on his enemies, also killing characters indirectly. Snape's tragic death was a peculiar case, though.
JKR uses the significance of the number 7 in many instances during the series. For example, seven years of magical education, seven trials to get to the sorcerer's stone, seven victims of the opening of chamber of secrets, seven horcruxes and so on.
Avada kadavra spell can be blocked by objects like statues, etc. (OoP). Now, Voldemort had already split his soul into different parts i.e. horcrux. So basically he had become immortal and therefore using the spell would not harm him.
In order to conjure the avada kedavra curse, you have to want to kill your victim. We all know that Voldemort could easily kill a child without an ounce of remorse... but not Snape. Snape didn't want to kill Dumbledore, and this was why the spell was blue instead of the usual green.
During his final confrontation with Voldemort, Harry knew that he (Harry) was the Elder Wand's true master. He again cast Expelliarmus, ejecting the wand from Voldemort's hand into his own as the Killing Curse rebounded off his body, fatally striking Voldemort.
Perhaps Voldemort's biggest mistake was thinking he was invincible. He was extremely arrogant and believed himself to be superior to everyone around him. Ever since he was a child in the orphanage, Voldemort thought he was better than everyone else. This sentiment continued to grow as he did.
Her sacrifice gave Harry the power of love, a protection spell sealed with the blood spilled by her death.
Ron never casts Avada Kedavra at Nagini in the books.
Speak to Sebastian in the Undercroft after this and he'll teach you any Unforgivable Curses you have missed up to that point, including Avada Kedavra. It's worth learning the curse as doing so should have no negative outcome on the game's story.
The darkest of the Dark Arts, Harry Potter unforgivable curses are the Cruciatus Curse, the Imperius Curse, and the Killing Curse. Although the curses are highly illegal, Harry using Unforgivable Curses happened, but he uses them once he was thrust into the Second Wizarding War.
Learning. Mastering Avada Kedavra is a very hard job. The killing curse is one of the hardest of all spells to learn and can only be perfected by very powerful witches and wizards. There is no particular way to say the curse, although you must cast it in a particular way.
Avada Kedavra backfired in Great hall because it met a counter spell (Expelliarmus) and Elder Wand recognising it's master didn't pressed the attack and resulted in counter fire.
Voldemort's greatest fear is death and as a result a boggart takes the form of his own corpse. It is unsurprising that this is Voldemort's biggest fear. After all, he did split his soul up encasing it in various horcruxes just so to keep himself from dying.
Dolores Umbridge is in a position of power and is allowed to stay in it even after abusing it. Lord Voldemort, on the other hand, is evil, whereas Umbridge believes she is one of the good ones and that her actions are justifiable, even necessary.
The "most faithful servant" is Barty Crouch Jr., who has already been in place at Hogwarts working for Voldemort.
When Harry wrestles Draco's “everyday” wand out of his hand at the Malfoy's mansion, he conquers Draco, and therefore the Elder Wand — hidden in Dumbledore's tomb at the time — transfers its allegiance to Harry. Rowling said her American editor suggested the moment when Harry conquers Draco should be more dramatic.
Alohomora, which is a spell that unlocks objects (and it's also Hermine Granger's signature spell).
Expelliarmus: Harry Potter's Signature Spell | Wizarding World.
Sectumsempra is a curse invented by Professor Severus Snape, during his childhood, when he was known as "The Half-Blood Prince". He created it with the intention of using it against his enemies, and it soon became one of his specialties.
Erroneously believing Snape is the master of the Elder Wand and that Snape's death will make him the master of the Wand, Voldemort kills Snape by having his pet snake Nagini bite him through the neck.
Quirrell didn't use the Killing Curse on Harry, because Voldemort said “use the boy” to get the Sorcerer's stone from the Mirror of Erised. If Quirrell had killed Harry right away, he would have lost the chance to get the stone.