A thought experiment:
- Make a high-level Magic-User.
- Don’t pick any spells yet.
- When you encounter some setback in the game, declare that your high-level character had spent months painstakingly researching a spell just for this occasion.
- On the spot, invent the ideal spell. This is pretty easy in Basic D&D: figure out the range (typically 60, 120, or 240 feet, or personal), the duration (usually 1 turn/level, 3 turns, or 6 turns), and the effect.
- The Dungeon Master then determines the spell’s level, whether it requires a save, etc.
- The spell “just happens” to have been in your load-out for this adventure.
- Give the spell an outlandish name. Chris Pound, as usual, has suggestions.
Once you’ve filled up all your slots on a particular magnitude of spells, guess what? Any spell which would be of that magnitude, is now one magnitude less. So: if you used up all your third magnitude slots already, and come to a conundrum that really needs a third magnitude spell to solve – guess what? you only have a second magnitude almost-but-not-quite-good-enough solution. The Dungeon Master is encouraged to reduce the spell’s magnitude by introducing an unwelcome complication rather than simply reducing the range or duration. You could, of course, avoid this complication by starting over with a higher magnitude spell, but it would occupies a more valuable slot which you might need later on when things really get ugly.
There seem to be few real-life examples of players actually researching new spells in Dungeons & Dragons, even though it’s been part of the rules since the dawn of time. This seems like a particulary fun way to go about it, and might make for a very entertaining 1:1 adventure. Given that Jack Vance’s Dying Earth characters always happened to have a contrived spell that was perfectly suited to any occasion (until late in the story when nothing seems to go quite as planned), this might be a way to mimic that effect.