Catch the Key!
You find yourself in another room, and apparently, you need to catch the correct flying key to get to another room. So, it's Quidditch all over again. This time there's no opposition, so you're free to catch it for all you want. The procedure is the same, except that you don't have to get within any golden circle (Stage 1).
"You grabbed the flying key! Now you can unlock the door and go on to the next room!"
Now go upwards, open the door and go through. Whoa, a checkerboard with pressure plates and chess pieces! You've got to make sure all the pressure plates (except one) are being held down by the chess pieces at one moment. When a chess piece moves onto a pressure plate, stop it with Flipendo. When you've done so, Ron moves onto the last plate, and you and Hermione go through the door ahead.
Go upwards to find Hermione and a cauldron. She tells you to find four Black Fire ingredients. There are four mazes to go through, each of which can be found at the corners of the room. They are easy enough to get through, but you must go through them in an order: Top Right, Bottom Right, Top Left, Bottom Left, getting all four ingredients. When you're done, go back to the cauldron in the middle. A pressure plate appears, and Hermione steps on it for you, while you use the Potion to get through the black fire ahead. Brace yourself...
You step through the fire to find...Quirrell! Well, if it isn't another double-crossing sonovabitch! He's a subject of the deadliest enemy of the world, Lord Voldemort, and has orders to kill you! After a brief, heated conversation, whatever remains of Voldemort screams, "SEIZE HIM!" (KILL HIM would have been more adequate) and Quirrell starts to run around.
Quirrell will be running around the whole room, casting curses at you when you get close, and they track your position!! Don't bother to attack Quirrell, but run behind the pillars in the room for shelter and let the curses hit the pillars until they break. They withstand two hits from curses, then shatter. Break all the pillars and the floor crumbles beneath you to Voldemort B!
This time, there are skulls on the floor, the Mirror of Erised in the middle of the room, and Quirrell is STILL running around the room casting curses, or enchanting skulls and sending them at you. See those snakes in the bottom right corner of the screen? Those are Quirrell's hit points, and you're supposed to use the Mirror to bounce off curses he casts at you to him! Dodge his flying skulls and use Flipendo on the mirror to flip it around so that you can bounce curses coming from the opposite direction. When he's destroyed, there's a great explosion...
Now, you are treated to several illustrations and an explanation about Quirrell's and Voldemort's, as well as Flamel's, involvement in the Sorcerer's Stone. Then...you are treated to a LAME ending, regardless of whether you win the most House Points or not.