The Mirror...

[Lord Chaos]

What in the heck do you use the mirror you find on level 2 for???

[Andy]

You use it to open the final door on the 'chamber of the guardian' room. It also is the answer for the riddle "I am all - I am none" A mirror is a reflection of everything that looks in it(all) but it is merely an image so is nothing (none).

Simple!