As for everyone's favourite child-bullying adult, Snape's Killing Curse was 'blue' due to the cyanish background of the film scene. It was actually green, but the camera and effects made a bluish overlay which overlapped the green spell.
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.
This is evident in each scene where the curse is evoked except for 1. When Hogwarts' Defense Against the Dark Arts teacher Severus Snape, kills headmaster Albus Dumbledore in Half-Blood Prince, the colour of his Avada Kedavra spell isn't the green we're accustomed to. Instead, it's blue in colour!
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.
The main significance of his death was that it bolstered Voldemort's trust in Snape. Dumbledore's death helped Snape regain the Dark Lord's trust, thereby making it easier for Snape to devise a successful plan to finally kill Voldemort.
Dumbledore had instructed him not to reveal anything to Harry until Voldemort was at his most vulnerable.
For the Potter uninitiated, “always” is how Snape explains to Dumbledore in the final book why his Patronus takes the same shape as the one belonging to his long-lost love: Harry Potter's mother, Lily.
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.
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.
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.
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.
He doesn't trust Snape as Dumbledore does, but he believes that he can detect any disloyalty. Moreover, Voldemort regards Snape as highly intelligent and therefore ' as a true Slytherin ' a person whose top priority is to take care of himself.
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.
Harry's signature spell is red, possibly representing gryfindor and everything good. Meanwhile, the killing curse is green because slytherin?
Voldemort believes that because Snape killed Dumbledore, the Elder Wand's allegiance lies with Snape. Although Voldemort is currently using the wand, he notes that it doesn't behave as it should for him. By killing Snape, he hopes that it will change its allegiance to him.
Voldemort thought Snape was the owner of the Elder Wand. Using Avada Kedavra while the Elder Wand was resisting Voldemort was already a risky business, but using it against the true owner would be suicide (as Voldemort would find out when he used the Elder Wand against its true owner: Harry).
There is likely a good reason that the Sectumsempra is not an unforgivable curse. It's mostly because Sectumsempra is Snape's personal curse that he created. It is not a widely known or used spell, and it is one that he kept secret — which means it can't be added to the list since no one really knows about it.
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.
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.
Many characters die in Harry Potter, but the series' most important deaths are arguably Lily and James Potter, Harry's parents. The couple perishes at Voldemort's hands, with Lily's sacrifice protecting Harry and tying his fate to the Dark Lord's.
Harry's scar had hurt during Arrival Feast because of Quirrell's connection to Voldemort; Snape was then talking to Quirrell, allowing Voldemort, from the back of Quirrell's head, to sense Harry's presence.
In the [Deathly Hallows] book, Snape's dying words to Harry were "Look at me". Right then we did not realize the significance of his words but in the very next chapter when Harry goes through Snape's memories in the Pensieve, he comes to know how much Snape loved Lily.
Similarly to Harry, Snape's patronus represents a person. In the memories he gives Harry before his death, Snape shows Dumbledore his patronus, using the form to prove his love of Lily Potter, Harry's mother. This indicates that Lily also had a doe patronus.
They were close friends, she saw in him someone special that she could care about. But she couldn't be with him. So, it seems like it was very unlikely that Lily ever found out Snape loved her.
Dumbledore reveals how thoroughly he loves Harry. Harry is brave, and Dumbledore is proud as any father would be. More than that, Dumbledore succumbs to a parent's weakness; he cares more about Harry's happiness and wellbeing than the wizarding world he is trying to protect.