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.
Dumbledore's Forceful Spell. Albus Dumbledore's forceful spell is a spell of his own invention intended to reveal the number of times one's soul has been split and detached and possibly even the location of those split soul fragments. It's like a weird version of Homenum Revelio but – you know – for souls.
Dumbledore then non-verbally casts a hydro-kinetic spell, where he draws the waters of the Fountain of Magical Brethren so that it erupts and flows out surrounding and encasing Lord Voldemort inside an enchanted sphere of water in an attempt to drown him and finish the duel.
Some would say there's no spell worse than Avada Kedavra, the Killing Curse that Voldemort used so indiscriminately.
Voldemort's signature spell was Avada Kedavra. Harry's was Expelliarmus.
The Killing Curse was created in the early Middle Ages by Dark witches and wizards. Primarily, the curse was used to quickly slay opponents during a duel. In 1707, the Wizards' Council was restructured into the Ministry of Magic, which allowed for more strict restrictions on certain types of magic.
Rictusempra, the Perpetual Tickling charm, which apparently can be stopped by the Finite Incantatem charm, was used by Harry against Malfoy in the Duelling Club. The intent was, of course, to tickle Malfoy to the point that he would be unable to jinx Harry in return.
'Piertotum Locomotor' The spell Piertotum Locomotor is an incantation used to bring inanimate objects and artifacts to life. Dumbledore uses this spell to bring statues to life to protect Harry against Bellatrix Lestrange (Helena Bonham Carter) and Voldemort's (Ralph Fiennes) killing curse.
In Rowling's Harry Potter series, Dumbledore demonstrated the ability to possess wandless magic on several occasions, most memorably when he cast Aresto Momentum without a wand to save Harry from falling to his death during a Quidditch match.
In the opening scene of The Secrets of Dumbledore, Albus Dumbledore (Jude Law) revealed that he was in fact in love with Gellert Grindelwald (Mads Mikkelsen) when they were teenagers, and the blood oath was a witness of their love.
Avada Kedavra
This spell is the favored one of Lord Voldemort. With it, he has claimed the lives of countless victims over the course of his long and infamous career as the most dangerous and feared Dark Wizard who ever lived.
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.
Expelliarmus did not beat Avada Kedavra.
Voldemort's wand (the elder wand) recognized its true master (that was Harry) and refused to attack it. In a way Voldemort killed himself as his own spell backfired on him.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
Additionally, in Harry Potter and the Chamber of Secrets, Professor Dumbledore looks right at Harry and Ron underneath the Invisibility Cloak while in Hagrid's hut, suggesting that Dumbledore might actually be able to see through the Invisibility Cloak.
Albus Percival Wulfric Brian Dumbledore was the only wizard Voldemort ever feared and the only one who could have defeated him in a duel. Albus Dumbledore is the most powerful wizard in the Harry Potter.
Avada Kedavra, also known as the Killing Curse, kills a person instantaneously and without injury. There is no countercurse for it, and only one person, Harry Potter, has ever survived it.
"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).
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.
Ginevra Weasley was well-known for her ability to cast a particularly potent Bat-Bogey Hex, which could be considered her signature spell as she used it several times on people who annoyed her and was referred as "an accomplished caster" of the spell.