Last week I proposed space scurvy, but deficiency diseases can also be interesting to consider in the context of a fantasy setting.
Imagine for a moment that fantastical creatures like dragons, basilisks, or medusa depend on some vitamin (or a complex of vitamins) which allow them to process magical energy or a “supernatural essence”. For the most part this is no big deal: This “magimin” exists as part of the natural food chain in fantasyland and these creatures get plenty of it from their natural diet. (Some of them might produce it naturally under certain conditions, just like we do with vitamin E from sunlight.)
But when these creatures start suffering from a magimin deficiency — for example, if a dragon starts eating livestock who have been raised in a natural antimagic field — things can turn bad. Our dragon, for example, might find his wings withering and falling off while his heart enlarges in an effort to cope with pumping blood through his great bulk. A medusa’s snakes wilt and become lifeless. A basilisk might slowly grow blind as its own eyes turn to stone.
A little too much science in your fantasy? Maybe. But I like to give thought to this sort of thing because it opens up interesting possibilities.
For example, what if we make the magimin deficiencies a little more magical? Without their magimins, dragons slowly begin to shrink… eventually becoming nothing more than large snakes. But what happens if a mad wizard were to superdose an ordinary snake with magimins… would they become a dragon (or some other insanely mutated creature)? Now we have a mechanism for those “mad scientist” wizards to use when they’re creating owlbears. And that means they need a supply of magimin. And gaining that magimin (by harvesting fairies, for example, or simply having it shipped in) will have consequences that can serve as adventure hooks (and also give the PCs non-standard ways of fighting back).
On the other end of the scale, what if magical creatures went away because their magimins went away? But if magimins were to be reintroduced to the food chain, suddenly we’d have a lot of dragons that have been trapped as snakes for a couple hundred years re-appearing.
cf wis in Ars Magica. It can be harvested from magical creatures, used to bind enchantments permanently and is a vital ingredient in potions of longevity.
Astral vampires are, I suppose, magimin uptake inhibitors.
I’ve actually considered running a variation of these rules before. Instead of a vitamin in their diet, magical nutrients are synthesized by the environment. Magical creatures that find themselves in a nutrient-poor environment suffer different effects. Dragons become ravenous and need to eat massive quantities of food daily to remain healthy, while demons can remain active only for short periods of time and need to slumber regularly to recover their strength. High-level characters also find themselves affected by this magic-starvation, and in order to protect themselves need to seal their powers.