Wild and Dead Magic

Within Danor’s borders, magic quickly seeps away, a consequence of the Great Malice, wherein the eladrin goddess Srasama died five hundred years ago. A creature’s own innate magical powers still function, such as a tiefling’s hellish rebuke or an eladrin’s fey step.
Creatures cannot cast spells or use magical class abilities unless they have some sort of permanent magic item as a focus. These items carry enough innate magic with them to power spells and prayers, but over a period of weeks or months, their power fades entirely. (As a guideline, common or uncommon items are disenchanted within a week; rare and very rare items within a few weeks; and legendary items might last a month or more, subject to GM adjudication.)
Until such time as they lose their enchantments, magic items brought to Danor function normally. In addition, rituals cannot be cast within Danor, though spells with the ritual tag can still be cast with spell slots. It is believed impossible to create magic items in Danor, so almost no Danorans study magic. The few Danoran mages there are either traveled to other nations to study, or purchased magic implements and paid exorbitant amounts to import tutors.
Just beyond Danor’s borders, in a broad swath hundreds of miles wide, the fabric of magic is damaged but not destroyed. In these places, known as the Malice Lands, whenever a character casts a spell (either from a class or an item) or activates some sort of magical class power, roll an unmodified 1d20. On a 1, a mishap occurs. This usually takes the form of the magic backfiring, manifesting as a freewilled monster, or otherwise going dangerously awry.