By the full moon the answer lies…

The full moon? Wolfs howl at the moon.

A potion will not rid of the disguise…

What disguise?

However, the effects are cured…

The effects of the disguise?

But only if the potion maker is lured…

Is the potion so hard that only one person knows how to make it?

I woke up, and it all clicked. Remus was always in and out of school and every time he came back he looked ill and sickly. Nivy Orson was the creator of the potion.

Remus was a werewolf.