Even though McGonagall is the Defence Against the Dark Arts teacher, she's unable to defeat the Potions master. It show's Snape's power. Yet not only does he refuse to fight back, he also seems to deliberately deflect one of McGonagall's spells into the path of two Death Eaters behind him. Then he flies away.
He didn't lose. Neither McGonagall's nor Flitwick's curses hit him, not even once, and at least McGonagall was shooting to kill. Severus was using defensive spells only: he didn't want to hurt them.
McGonagall was initially appointed as Headmistress, but was demoted after Voldemort took control of the school and placed Snape as Headmaster.
In the Harry Potter series, had Minerva McGonagall and Severus Snape both gone all out in a duel, who would have won? Severus Snape would win hands down, as evidenced by the clash of the seventh book or the eighth film.
Professor McGonagall did not know. It took her by surprise just as it took Harry by surprise.
When McGonagall calls Snape a coward, she is not referring to his skills. She is in fact attacking his ethics and morals. From Harry and Co.'s perspective, Dumbledore was weak and alone and begging Snape to not kill him.
Dumbledore himself was aware of Snape's actions and trusted him to aid him in his mission. He also shared some information with Harry regarding Snape's true loyalty and role in his plan, but only toward the end of the series. Everyone who worked for the Order knew Dumbledore trusted Severus.
It is possible that this spell is Incendio Duo or Incendio Tria, given that both spells are used to create a large amount of intense flames, and that both are commonly used in Duels.
For example, in Harry Potter and the Deathly Hallows – Part 2, Snape was reluctant to fight McGonagall when the latter took him to a duel in front of Hogwarts students. Both characters had their strengths, but the last Harry Potter movie proved Snape was the strongest Hogwarts professor.
Winner: Snape
The kind of versatility in magical abilities that Snape displayed was almost around the level of Albus Dumbledore and Voldemort, making him easily more powerful than the average wizard and even the members of the Order of the Phoenix and the Death Eaters.
History of Slytherin
The Head of Slytherin is Horace Slughorn (who left the role to Severus Snape for fifteen years before taking it up again in 1996) and the House's patron ghost is the Bloody Baron.
McGonagall didn't join the Order of the Phoenix at first because she was spying for the Ministry of Magic. While we know in Harry Potter and the Order of the Phoenix that Minerva McGonagall was new to the Order, we didn't know why she didn't join during Voldemort's first rise to power.
Hogwarts students
Despite being Headmaster, Black was known to dislike most of the students of Hogwarts, and had no real ambition to be seen as a role model or any interest in the students' education. This was possibly a reason why Sirius Black believed he was the least popular Headmaster Hogwarts ever had.
He would always resent Harry for being James' son instead of his. Snape even said that he didn't want anyone to find out that he was protecting Lily's child, “especially Potter's son” (pg. 679 of Harry Potter and the Deathly Hallows) because of his hatred for James.
McGonagall followed up Harry's action by using the Imperius Curse on Amycus before tying him up with a net, rendering him useless during the Battle of Hogwarts.
Professor McGonagall is a Death Eater
According to the theory, McGonagall's seeming disregard for Harry Potter's safety, her talent for transfiguration, and and her stoic nature all point to the fact that she was a Death Eater.
Weaknesses. McGonagall is never portrayed as having any particular weaknesses. Her stern facade likely prevents anyone from getting close to her emotionally, with the possible exception of Dumbledore. We are led to believe that she prefers her solitude.
Why didn't Dumbledore tell Snape about the Elder Wand so Snape could break it before Voldemort found it? The answer is simple: It was far too risky for Severus Snape to be aware of both the Hallows and the Horcruxes.
Therefore, figuring out a spell that is Draco's favorite is hard and, in the movies, there is no defining moment that cements a spell as his favorite. Based on Harry Potter lore, and an article by The Healthy Journal, Draco's signature spell is a N.E.W.T standard spell, The Protean Charm.
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.
None of the pupils had the power to cast Avada Kedavra. Not even McGonagall could cast it, and she was duelling to kill - she said so herself.
Snape's fierce devotion to and love of his childhood friend Lily, Harry's mother, is the foundation of that loyalty. After Harry Potter and the Half-Blood Prince, Snape's loyalty was a matter of intense debate among the fans.
There were many things Snape actually liked, but probably only one he ever truly loved. Look no further than his Patronus, which remained a doe even after all those years. Though she left this world, Lily Evans never left Snape's heart. For many, it was proof that he had one to begin with.
Severus Snape spent the majority of his life in love with Lily Potter. It is easy to understand why Snape, who had an unhappy homelife as a child, fell hard for the first person to show him love and kindness.