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.
McGonagall then defeated Severus Snape and banished him from Hogwarts and began to defend the school.
Minerva McGonagall
A total badass. She's the Head of Gryffindor and the most powerful witch in Hogwarts.
Voldemort is viewed as the most powerful wizard in Harry Potter, but that title should really be given to Professor Severus Snape. When you think about powerful wizards, especially in the Harry Potter universe, you will likely put Voldemort at the top of the list. After all, the Dark Lord was the big threat.
Additionally, Snape is more skilled in potions than Dumbledore, making him a powerful contender for Albus's spot on the list. Albus, however, edges out Snape thanks to the former's greater base power, and deeper understanding of the complexities of “old” magic.
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.
However, in a sudden turn of events, Snape chose not to fire but only defend himself. What remained unnoticed was — how he deflected McGonagall's spell killing the two Death Eaters standing behind him, before flying away to make sure that everyone around would stay safe.
Winner: Snape
Bellatrix would be in the top pile of witches and wizards of all-time based on powers, but her reliance on the same moves and lack of wit means she would be defeated by Snape after giving him an initially tricky time.
Severus Snape might have pretended to serve Voldemort (while in fact, as we all know, working as a double agent for Dumbledore), but there's almost no question he was more powerful than the Dark Lord.
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.
Bellatrix is (kind of) in her prime, while McGonagall is old. We should also know that although Bellatrix is evil, it doesn't mean she's stupid. But seeing that McGonagall is old, we can correctly assume that she's experienced. I'd say McGonagall wins the duel, no questions asked.
SHE'S A PROFICIENT AND POWERFUL WITCH
J.K. Rowling has stated one of the reasons Ginny is gifted is due to the fact she was a seventh child and the first female Weasley born in generations, which ties into the superstition of the seventh daughter of a seventh daughter.
Outnumbered, Snape dashes into a deserted classroom where a loud crash is heard. Pursuing, McGonagall screams, "Coward!" Uncloaked, Harry and Luna rush inside, startling the other professors. Snape has leaped out the window.
Snape was in a very unique position. Dumbledore made the best deal ever with him. He offered nothing and in return gained the loyalty of a high rank Death Eater. Both Narcissa and Draco stated that Snape was the Dark Lord's favourite and not even Bella denied it.
Minerva McGonagall
McGonagall was among the oldest and most experienced teachers in Hogwarts, and she was a worthy successor to Dumbledore as the headmistress. In fact, she has proven her mettle against Voldemort and survived a duel against him.
Of the characters in the books, the top-tier wizards are pretty clearly shown to be Dumbledore, Voldemort, and Grindelwald. If one accepts that magic has advanced since ancient times, these three are probably even greater than the Hogwarts Founders themselves.
It is interesting also to note that Harry does not actually kill Pettigrew, but that Voldemort's gift kills him despite Harry's efforts to save him. Pettigrew's death is a reaction to his own attempt to kill, or at least, disable Harry, coupled with Voldemort's distrust of his own lieutenant.
Mostly because James died and Sirius was sent to Azkaban for 12 years, while he was still growing in power, skill and precision. That said, Severus' magic far outclasses that of Sirius. Granted, Black's more of a natural when it comes to duelling, but he's nowhere near as accomplished as a wizard.
Dumbledore may have been a legendary wizard, but he can't be compared to, well, Merlin, a wizard so legendary even Muggles know of his exploits. Merlin was the world's most famous wizard, and, arguably, the world's most powerful. Fellow Slytherins, you can be proud of our house— the great Merlin himself was one of us!
1. Albus Dumbledore. Image via Warner Bros.
Once again, the trio had the wrong end of the broomstick. Snape was trying to prevent the Stone from falling into the wrong hands. Unfortunately, he was a distraction from the real threat: nobody suspected Quirrell while his colleague was 'swooping around like an overgrown bat'.
Originally Answered: How did Umbridge and other ministry members mange to get away with attacking Professor McGonagall in book 5? As Minister of Magic, Fudge was adamant to believe that Voldemort had returned.
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.