First, gather up all the coins you can in here. There are a lot of them!

Use the rat in the top left area to get the pink thing - put it into the cauldron.

Unwind the snake and pull out its tooth - put that into the cauldron.

In the bottom right, zap the gold area to see a skeleton dancing. Take his arm and add it into the cauldron. Now the potion is ready.

You get a gold brick (15/200) for drinking the strength potion and opening the door.

When you're ready to leave the classroom, go out the door to the bottom left of the room. Follow the ghostly guy. You'll go back through the courtyard. Make sure you destroy the statues around the fountains to have the fountain make lots of lovely flowers!

If you've bought stupefy from the shops, now is a good time to stupefy the bully-boys and save the Student In Peril. Then light-blast the vines in the bottom left, to go on to your herbology class!

Lego Harry Potter Walkthrough