Locheil on the GLOG discord had a good idea:
So I've decided to write it. Since it's in the GLOG discord, I'll obviously write it as GLOG classes. But I think it would probably work best as half-classes, 2 templates with a delta requirement.
(the deltas preclude magically guaranteed outcomes, so an actual prophetic dream doesn't count for the Lunar Arts, and a magic rock that makes people view it as valuable doesn't count for the Mercuric Arts)
Lunar Arts
Δ: Have a dream of yours literally come true, by chance or by effort (ask your DM for random dreams)
A: Select an art form. Works you make in that medium can either provoke an emotion of your choice, or make those who view them for more than d6 rounds save or fall asleep and have dreams of your choice. Artworks must be prepared as a downtime action (whether painting a picture, writing a song, etc.)
B: Gain an MD and an Illusionist spell. You regain this MD by meditating on the moon, and cannot regain it on nights of a new moon.
The Lunar Arts are practiced in urban monasteries by artist monks who sleep based on the moon, rather than the sun, and who record their dreams.
Mercurial Arts
Δ: Trade or sell something for 10 times its worth
A: Once per day, you can convey an impression telepathically to someone you've met before, regardless of distance. If it wouldn't work, its not expended. You can also run a marathon at your normal running speed. You'll be exhausted at the end, and if you are carrying significant weight you can only run half as far.
B: You can squeeze through any space that can fit your skull, and learn an (expensive, illegal, toxic) recipe for a potion which will cause 1 lie you say to be fully believed by anyone who hears it.
The Mercurial Arts are practiced by itinerant monks, who have no qualms about profiting off their expertise, and are generally mistrusted.
Venerian Arts
Δ: Have 3 people in love with you at once, or perform a really significant sacrifice for the person you love most (DM will tell you if this has happened, don't do something little and then pester the DM)
A: You learn a rite by which you can bless a field, orchard, or vineyard to provide triple its normal produce. Its kinda gross though. Requires one other person.
B: Your knowledge of anatomy qualifies you to be a surgeon. Increase your damage with unarmed attacks and knives by 2 steps (1 → d4, d4 → d8). You can bless an additional field etc.
The Venerian Arts are learned by temple prostitutes and certain farmers. They ritually drink vinegar, and meditate with incense and the music of stringed instruments. Obviously they are highly sought after.
Solar Arts
Δ: Ingest a pound of gold over a period of seven days, and meditate for the whole seventh day
A: For feats of strength (but not attacks) you count as Strength 20. Reduce this effective strength by any amount to produce a blast of blue chi dealing twice that much damage, which cannot miss. You have to wait a round before using this again. Reducing it by more than 10 takes a round to charge. Recovering this strength takes a day of meditation (sunup to sundown).
B: Reduce your effective strength by any amount to fly for 10 minutes per point at your regular running speed.
The Solar Arts are practiced in isolated monasteries, which are attended and patronized by noble second sons. While the monasteries are actually pretty spiritual, the threat of 20+ flying laser warriors who can punch through an oak portcullis means that temporal powers don't tend to cross them.
Martial Arts
Δ: Fight 10 men to the death.
A: You cannot fumble with any weapon.
B: Any group you lead counts as half the size for logistical purposes, and twice the size for positioning purposes (i.e. flanking and sieges etc.)
You don't need me to tell you who practices martial arts.