She most definitely used Expulsa. It's said that it was a powerful Stupefying spell, but that would just put the opponent to sleep for a longer time than a Stupefying spell from a 1st year. I don't know why people think it was Avada Kedavra or why they are saying that it's not a known spell.
No, we don't know what spell did Molly use to take down Bellatrix, but it certainly wasn't Avada Kedavra.
None of the good guys dare use the Killing Curse throughout the events of the movies and books, no matter how high the stakes and how difficult things are. But Ron Weasley is the exception, giving it a go in the Deathly Hallows: Part 2 movie when himself and Hermione look destined to die via Nagini.
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
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.
Imperius Curse ('Imperio')
The first of the three Unforgivable Curses, Imperius gives the spell-caster total control over their subject. As fake-Moody explains as he demonstrates on a spider: 'I could make it jump out of the window, drown itself, throw itself down one of your throats…'
In the film, Bellatrix casts a blue spell at Ginny Weasley instead of a Killing Curse, who deflects it using a Shield Charm. In the book she just avoids it.
5 Bellatrix Lestrange: The Cruciatus Curse.
Harry James Potter holds half-blood status in Rowling's imagined wizarding world because his mother is Muggle-born and his father is pure-blood.
As the youngest Weasley, we're sure Ginny observed more than her fair share of unpleasant spells over the years but it was the Bat Bogey Hex she was famous for – and with good reason.
Malfoy spots Harry and casts a Cruciatus curse; Harry, defending himself, using the Half-Blood Prince's Sectumsempra spell without knowing its effects. To his horror, it gashes Draco's face and chest, spilling his blood everywhere.
Avada Kedavra
It's used to kill people, it's an Unforgivable Curse, and it was Voldemort's favourite, so it's going last.
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.
Sectumsempra was a curse invented by Professor Severus Snape that lacerates the target and causes severe haemorrhaging. Snape created it as a student of Hogwarts, with the intention of using it against his enemies, likely including the Marauders, and it became one of his specialities.
Because he didn't believe disarming him would be enough. After Dumbledore was dead, Voldemort would have been told everything. Including the fact that Draco disarmed Dumbledore. But all he cared about was who KILLED Dumbledore.
"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."
Alohomora, which is a spell that unlocks objects (and it's also Hermine Granger's signature spell).
In Deathly Hallows, Hermione faced a real test of her physical and psychological stamina. After being on the run from a bunch of Snatchers, the gang were taken to Malfoy Manor, where Bellatrix proceeded to torture Hermione using the Cruciatus Curse.
Firestorm. Firestorm was a spell that created a large ring of fire around the caster's wand. This spell is one of the last and most powerful spells that Albus Dumbledore cast using the elder wand before his death.
Hermione cast a bluebell flame that could be carried around in a jar. She used it to set Snape's robes on fire during the match between Gryffindor and Slytherin of her first year. Hermione used this spell against Devil's Snare when she, Harry, and Ron worked through the challenges surrounding the Philosopher's Stone.
Dudley's last line is also found in a deleted scene.
His last words in the movie are, "I still don't understand why we have to leave." But he also has a deleted film scene where he has a final conversation with Harry, and his last line is, "I don't think you're a waste of space."
Also known as the Leg-Locker Curse, this spell is used on Neville by Malfoy, although we don't know the incantation until Hermione whispers it to Ron.
Harry became so enamoured with the spell that he eventually used it to finish off Lord Voldemort. Here's how Harry's relationship with Expelliarmus became his signature – and why that's a good and bad thing.
What Is Dumbledore signature spell? There were two; Apparation and Invisibility. Dumbledore must have used these particular skills thousands of time in his lifetime for any number of purposes. His vast gathering of knowledge probably came as a result of his skill in appearing and disappearing at will and unseen.