Magical Overabundance

Magic, the powerful and transformative substance it is, is found in trace amounts in the blood of all living creatures, the roots of all plants, and diluted in all waters. This trace amount of magic is what allows spells to be cast, potions to be brewed, and artifacts to be enchanted. Over the course of a normal sapient life, the magical intake from drinking and eating is so minimal and spread out that it doesn't affect a living thing, beyond recharging their own magical well over time. However, rapidly increasing the amount of magic absorbed by the body in short succession can cause a variety of transformative and debilitating effects, all collectively known as Magical Overabundance.

Causes

This can happen in a variety of ways. Certain places in the world are polluted with excess magic, exposure to which can cause Overabundance. The Heart of the World, the island where the Fallen Heart rests, is the most notorious of these places. Reports stretching back hundreds of years speak of how explorers were afflicted with Overabundance within a matter of minutes of stepping on the saturated magical sands.
Magicite crystals, when used too rapidly or too frequently to restore magic to the user, can cause minor versions of Overabundance. This typically occurs over years of dedicated and repeated use, and those who burst a crystal on rare occasions for defense or neccesity are typically safe. Decades ago, there were stories from Oroi about a mine worker who fell into a Magicite geode the size of a house, shattering hundreds of crystals all at once with his heavy mining tools and instantly becoming overwhelmed with magic.

Symptoms

The powerful mutational abilities of magic, the same that allow lead to be turned to gold or a Timus to shapeshift into an owlbear, cause sudden and irreversible changes to the physique of those afflicted by Magical Overabundance.
Phsyical Symptoms: The doubling or reshaping of limbs, excess digits or teeth, changes in size, sudden patches of new fur or scales, fleshy growths, additional organs, extra tails or wings, goo-like physique, or new fur or feather colors.
Mental Symptoms: Auditory and visual hallucinations, insatiable appetite, desire to consume raw magic, ability to see through time, false memories, continuous mind-reading, shifts in language capabilities, innate spellcasting, erasure of the mind, beastly behavior, new senses, emotional outbursts or detachment, and fatigue.