If one abides by the rules set forth in OD&D (and later, Moldvay/Cook), Magic-users and Elves only gain new spells for their spellbooks by advancing in level or creating new spells through research. The explanation of this acquisition of new spells upon level advancement is left vague, perhaps by accident or design, but the default assumption in many campaigns is that these spells are received from either the mages guild or the character’s teacher. That’s a perfectly rational way to explain these newly gained enchantments and it has the benefit of not requiring much on the part of the referee.
But what if the referee and players aren’t looking for rational explanations and intend to plumb the depths of the weird to account for these sudden gains of mystical knowledge? In that case, one might get something like the list below. Provided here are some ideas for sources other than the magic-users guild from which spell casters might learn their new spells upon level advancement. Some may be more appropriate than others for one’s homegrown campaign world, but it’s always an interesting exercise to think outside of one’s comfort zone. You never know what you might find there to tickle your fancy.
Aliens: Magic comes from space, don’t you know? The only way to gain new mystical knowledge is through the suppliers. Upon gaining a new level, the spell caster must make contact with one of the races from beyond the Cold Void and negotiate for arcane enlightenment. These aliens could be Lovecraftian horrors, enigmatic Greys, or even benevolent E.T.s. Even better, they’re never seen firsthand. Upon reaching a new level, the spell caster must wait in an open field where a “burning wheel” will appear in the night sky above him. A beam of light shines forth from the wheel and the caster vanishes. Several hours later, missing memories of where he’s been but with a new spell in his memory, the caster reappears.
Ancient Monuments: Inscribed on a leaning stele or carved into the face of a mountain are ancient formulae for magical spells. Once found, these inscriptions provide an instantaneous transference of mystical knowledge to the reader, allowing them to gain new insights into the arcane and providing them with a fresh spell to add to their spellbook. Finding these antique monuments can be as easy or as difficult as the referee desires. Particularly cruel referees might want to reread “The Other Gods” by H.P. Lovecraft before putting this method into play.
Animals: Taking a page from Leiber, let’s assume that each animal species is ruled by an intelligent paragon who guides and protects the lesser specimens of its ilk. The caster must seek out this paramount of animals in order to learn magics specific to these creatures. Web might be taught by the Baroness of Spiders, move earth is gained from the Duke of Badgers, and fly can only be learned from the King Bee.
Consumables: Certain meals prepared by chefs trained in esoteric techniques provide nourishment for not only the body but the psyche as well. While finding and negotiating the services of such culinary masters is not always easy or cheap, once enlisted, these chefs can provide the caster with feasts that result in new mystical knowledge. Other consumable possibilities include vessels that contain glowing, liquid mana, which beg to be drunk or even “magic pills” or injections waiting to be plundered from the ruins of the Ancient Ones.
Devils & Angels: Summoning extraplanar creatures to serve as instructors of the mystical is another fantasy cliché. For a low level spell, a minor imp or devilkin might serve as a tutor. Higher level magics will, of course, require the caster to deal with entities of much greater power and therefore a much greater price. For those who are concerned with the state of their immortal souls, a more benign source might be preferred, requiring the assistance of a local, “mage-friendly” church to contact them. A variation on this theme might be, to paraphrase Gaiman and Pratchett, an angel who “not so much as fell as sauntered vaguely downward.” This disgraced (literally) angel is seeking to get back into the good graces of the Divine and assists mortals in need at little or no cost, provided they work for the betterment of all.
The Faerie: When magic isn’t a product of space, it likely comes from the Summerlands, and the Good Folk are the one who can teach it. Such unearthly mentors could be drawn from the Seelie or Unseelie Courts, found beneath the mounds that dot the heath, or even reside in one’s own barn, where they perform minor services in return for a bowl of fresh milk. Would-be students are warned that the Faerie often abide by strict, but irrational laws, and to break these rules is to come to a very bad end.
Immersion: The concept of immersion in a body of water has traditional ties with both new life and sorcery (see accounts of baptism rites and witchcraft trials). High in the mountains lays a pool that is fed by a dancing cascade of waters. On nights of the full moon, bathing is this pool provides spell casters with an influx of mystical teachings that impart a new spell into their realm of understanding. While water is traditional, liquid reservoirs composed of blood, oil, or ever proto-matter are just as likely candidates for imbuing one with mystical lore.
Psychotropic Drugs: Certain obscure substances break down the barriers between the mundane world and the unseen fabric of the multiverse. Imbibing in such substance grants the spell caster insights into a much larger world and allows them to make great leaps of cognitive thinking. The results of such mystical journeys are new spells to bolster the caster’s repertoire. These psychotropic substances might be Melnibonéan sorcerer-drugs, exotic plants from East, or even the correct species of amphibians that live in the Great Miasmic Swamp.
Physical Trial: Drugs are not the only way by which the barriers between worlds can be breached. A less pharmaceutical, but more painful method is through physical denial or self-induced suffering. Fasting in the wilderness to the point of hallucination, self-flagellation, enforced sensory deprivation, or the traditional “bed of nails” may each provide the caster with fresh mystical understanding, provided he survives the process. Referees looking to equate great mystical power at the expense of the physical form are encouraged to give this method some consideration.
Tattooing: A subset of the Physical Trial, the cliché of magical tattoos has been around for as long as the art itself. Upon gaining a new level, the caster seeks out an enigmatic foreigner who practices his art down on the seedy waterfront. Catering to spell casters alone, this tattoo artist draws his designs from a collected catalogue of formulae and symbols dating back to the dawn of time. Each grants access to previously unknown magics. For referees who require that new spells are determined randomly, rather than chosen by the player, the oft-repeated story of drinking heavily and then getting a regrettable tattoo might explain why the caster decided that water breathing, instead of fireball, was going to be his first 3rd level spell.