Defeating The Giant Mother Spider:

To get to it, use your Lumos spell to light the floor and follow the trail of spiders. Unlike the book, the spiders that are not normal size will try to kill you. Attack them with Incendio. When fighting the Giant Mother Spider, do not try to hurt the spider itself. Instead, use your Incendio spell to burn the web it has attached to the various trees. When done, it will fall into the pit and you will slip in after it. In here, just run around until it rears its head and exposes its soft under-belly. It is the only part that is susceptible to second level magic. Note: It is best to not charge and use rapid firing to get a little extra damage.