Random Magical Breakthrough Table

A bleary-eyed Xag-Ya emerges from a set of catoptromantic mirrors that your
wizard invented by accident.

A wizard in your game is researching spells or trying to make a magical item. Or, I dunno, researching some aspect of the Dreams Of Ruin. They fail at whatever they were attempting, but as the DM you want them to have discovered something. "Nothing" is the most boring result possible from any game mechanic.

Polish off that d8 and give the players something to chew on:

1. A simple recipe for spontaneous generation. The animal should be something like a toad or a lagomorph, and the ingredients should involve stuff like bundles of rotten reeds, salt, and moonlight. The recipes only require 1d4 hours per batch of 2d20 varmints.
2. A simple method for condensing 1 hit die skeletons into the shape of an oversized bone arrow. The process costs about 10 gold, but it produces an arrow that will unfold into a very angry skeleton. Could it be helpful for sieges? Probably not!
3. A weird variation of a spell that the player already has. Ad hoc choose what you perceive to be the player's favorite damage spell, then change the damage type (this version does electric damage) and tell the player that every time they cast it, they teleport 10 feet in addition to the usual effects.
4. The wizard invents a musical note that shatters wood. If they are a plausible vocalist, they can shatter a single board with their voice. With a specially designed dungchen they could probably bust down a door.
5. Hurray! The wizard discovers a questionable application of the third homeopathic principle. They can now dilute a 1d8+5 healing potion into two 1d6+1 healing potions. I assume your potions heal different amounts than in my campaign, so tweak the numbers. Remember that it's only kind of an innovation.
6. The wizard designs schematics for a set of catoptromantic mirrors. They would cost about 300 gold pieces in my game, and be useful for increasing the range of divination spells. An interesting and definitely unintended feature of these mirrors is that a xag-ya will emerge from them every 1d4 days and wander around for a bit before zipping back into the mirrors. A xag-ya might have some application with magic item creation (who wouldn't want a sword with one of these trapped in it) or powering an improbable wizard project of some sort (they are basically sentient batteries). An interested wizard with these schematics could probably spend a few weeks designing a set of obsidian mirrors that would produce xag-yi instead of xag-ya. One thing is for sure: xag-yi and xag-ya fucking hate each other.
7. The wizard discovers a better way to cast an existing spell. Arbitrarily choose a spell that you think is too high level for what it does and tell the wizard they can memorize it as though it were a level lower. For example, based on my reading the tiny hut spell (a 3rd-level spell) is much, much worse than rope trick (a 2nd-level spell). I might tell the wizard that they have discovered a way to cast tiny hut as a 1st-level spell. Seriously, what is up with that spell?
8. Birds are incredibly receptive to sympathetic magic. The wizard realizes that if they cast their spells just so, a number of game birds equal to the spell level expended will be summoned.