Most of the previous levels had been designed by Tom and remained largely unchanged, but in Snape's case, nothing had changed.
The only way through was to solve the riddle, so Tom began to think and finally deduced that taking the potion from the smaller bottle would let him cross the flames to get to the last level, and the round bottle at the far right end of the line would get him safely behind the flames to the previous level. And Tom had no doubt that Snape had put poison in the other bottles: he was a ruthless man.
"To go forward, you need the magic potion from the small bottle, to go back, you need to drink the magic potion from the round bottle." Tom shared his reasoning with Professor McGonagall, who checked it, found no mistake, and then picked up the aforementioned potion bottle."
The bottles were all different sizes and contained enough potion for five or six people to take a sip each.
Professor McGonagall looked at Tom, "You can come back."
To Tom's surprise, Professor McGonagall didn't want him to face any more danger. But Tom didn't panic, "Professor Dumbledore asked you to do that? I'm indispensable for the last obstacle, too."
Professor McGonagall blushed: indeed, Dumbledore had only said to take Tom with her, but he hadn't really told her to ask Tom to come back before the final level....
"Maybe the boy really is the key link to the final level." Professor McGonagall thought helplessly, it was hard to guess what Dumbledore was thinking and she didn't want to spoil Dumbledore's plans by taking matters into her own hands.
Was Tom the key to the last level? of course not! The last level was the Mirror of Erised, which required someone who knew the effect of the Philosopher's Stone, but did not desire it, only then could one obtain the Philosopher's Stone. How could a boy like Tom, who is so desperate for money, not desire the Philosopher's Stone?
He can turn things into gold! That is the greatest achievement of alchemy! If he can study it...
The word "Philosopher's Stone" was all it took to arouse Tom's desire.
But Professor McGonagall didn't know that, sighed and agreed with Tom, but insisted that he stand behind her, and made him promise to be careful.
Professor McGonagall drank the potion and walked through the flames. Tom followed her lead, but waited a little longer, took out his teapot in advance, and popped the Occamy into his mouth.
The magic potion was like ice, protecting the whole body at once and allowing the drinker to go through the flames without feeling the heat.
Professor McGonagall stepped through the flames and into the last room, where a familiar figure appeared before her eyes.
It was Quirrell.
He stood in front of Erised's magic mirror, his face serious and his gaze deep. Instead of his usual scowl and antics, he looked calm and deep.
"Indeed, it is you, Quirinus" Professor McGonagall let out a sigh of relief as if to confirm something. She didn't want to run into Snape here.
"I can't believe it's you, I thought it would be the big bat Snape!" Whenever Quirrell spoke, he always stuttered, but now, he didn't stutter at all.
"Severus..."
Quirrell suddenly burst out laughing, "Now that I have Professor Snape to thank for! Thanks to Snape, sniffing around with his hawk nose, attracting all the attention. Who else in the school would suspect that poor, stuttering Professor Quirrell? Snape is to be congratulated!"
Quirrell laughed hysterically, as if he couldn't breathe "And the supposed savior, Harry Potter, is still spying on Snape, isn't he? How can such a man, defeat the master? Supposedly 'love'?"
"Master?" Professor McGonagall's eyes narrowed.
"Yes, Master!" Quirrell's expression went wild, "The Grandmaster has given me knowledge! I am now stronger than ever. Dumbledore is old, he is like a candle in the wind, but my master is eternal."
Quirrell whipped out his wand, "Minerva, submit to my master, and a place may be reserved for you at his side."
He was answered by a red light from the tip of Professor McGonagall's wand, but it was pushed away by a wave of Quirrell's hand. Quirrell's eyes were now more like the pupils of a snake, and his pupils had grown long and thin. It was clear that the weakened Voldemort had given him something to work with, even if he could not fight directly.
Now Quirrell's self-confidence was at an all-time high.
In the past, Quirrell had been no match for the veteran Professor McGonagall, but after Voldy's careful training, Quirrell's strength had skyrocketed and he was now capable of fighting head-on with Professor McGonagall.
By now the two had exchanged spells several times, switching positions, and Quirrell was approaching the burning door.
Suddenly, a huge dog's head came out of the door, followed by two large hairy paws, and Quirrell was quick enough to roll and avoid the bite, but the paws left a deep gash in his leg.
Quirrell cast a spell again, hitting Tom hard on the left side of the dog's head, leaving him with a cut the size of a bowl. Tom's transformation into a three-headed dog had increased his size and reduced his agility. But despite the attack, Tom managed to charge into the fray.
Quirrell's spell looked very impressive, but the actual damage was very limited. It looked like half a dog's head had been blown off, with the bones showing, but in reality it didn't even hurt: as long as Tom wouldn't change his consciousness: it was just two pieces of solid flesh.
Tom lunged at Quirrell with great bravery, and Quirrell cast spells, but Professor McGonagall did not stand idly by and turned the stones scattered on the ground into various weapons and fired them at Quirrell.
In an instant, Quirrell lost his concentration and was left in a terrible state, with several bloody holes in his body. But the unicorn blood he had drunk earlier took effect, and the superficial wounds healed quickly, and Voldemort, within himself, began to power up, pouring his accumulated power into Quirrell's body.
With bloodshot eyes, Quirrell roared and cast the spell (Protego), deflecting Professor McGonagall's spell and other strange weapons, while with his other hand he snapped his fingers and several ropes emerged from nowhere, nimbly wrapping around Tom's claws and binding him.
The dual use of his magic had taken an enormous toll on him, almost exhausting him at that moment: it was extremely difficult to conjure ropes strong enough to bind a three-headed dog, and to summon the spell (Protego) that could deflect Professor McGonagall's attacks.
But it was worth it.
"Phew, phew..." Quirrell didn't speak like a villain, but turned a broken stone on the ground into a short sword the moment he bound Tom, and used a spell to drive the sword through the three-headed dog's head in the middle. During the fight, he had noticed something unusual about the three-headed dog: of the three heads, only the middle one was conscious.
Quirrell didn't know if this was normal, but that didn't stop him from blowing the middle dog's head off.
Quirrell smiled happily as he watched the light fade from the dog's eyes.