Animals have parasites and diseases, so do plants, there are even bacteria that cann dissolve oil spills or plastic or what have you - why couldn't there be a disease living off magic - a magic item could be infected, losing power and speading the plague to other equipment it contacts, while a magic user would slowly lose his powers and contaminate all he works with or casts a spell at...
The extra-planar citadel of Ansern is named after its mage-founder. Ansern discovered the means to traverse the planar gulfs and created the citadel as a haven for his disciples in the art of planar-exploration. The disciples of Ansern continue his work and explore the countless worlds opened up to them by the work of the mage. They are cataloguing everything they discover in preparation for the greatest volume ever written: the Mondopedia, a book detailing many of the worlds. But the countlessness of the planes means that their book will never be finished.