They are vivaporous. Young are born after eleven months of gestation and, for the first couple years of their lives, feed on leaf-like material called "lish" that grows from the skin of their parents. All adults produce some amount of lish throughout their lives (though it tends to become tough and bitter in old age). A hormone stimulates lish production in females shortly before they give birth. Another hormonal feedback loop causes both males and females will produce more lish if something is consuming it, and to reduce production if it is not being consumed.
Rename "dryants" to something derived from Myrrha or Adonis? Or maybe use such names for places associated with dryants?
Creatures based on classical Chinese story of Xuanxang and the Monkey King? https://thehistoryofchina.wordpress.com/2016/02/21/90-special-monkey-business/
City of Innsmouthe, primarily populated by undine.
Shadows never lie; they always tell the truth (except in REGION, where the shadows lie). Shadow-projection and shadow-manipulation spells. Shadows are mostly harmless, but make excellent scouts. Rules around how shadows deal with bright light, total darkness. With the right magic, shadows can deliver touch spells.
Shadowcats: medium-sized cats with natural attacks that can damage shadows. The can also detect shadows in the dark. They won't usually bother ordinary shadows, but may play with shadows that are moving around a lot. Damage to ordinary shadows is usually harmless. Popular as pets.
For unclear reasons, dragons are almost always hoarders. They can hoard the strangest things.
Zalgo, Slenderman, other creepypasta, He Who Waits Below (often inscribed underneath or on the bottom of other gods' altars), The Taker Of Eyes (appears as a waxwork clown with gaping voids for eyes)
The Nine Bows
Need some place with a divine monarchy. Conflict between the government and people who insist that only the "real" gods may be worshipped. On an island, relatively little contact with outside
Two states that are currently at an uneasy truce in a long-running war.
Region with a collapsed government, ruled by warlords (Sengoku Japan, Warring States China, Migration Period Europe, etc.)
Casting illusions of dragons is illegal in the dragon-states
Visible illusions (figments, patterns, glamers) are low-level evocation? Can make illusions out of dust and smoke using transmutation, but difficult to make realistic images Projecting images into people's minds (phantasms) is enchantment
Underground ecosystems driven by radiation. Glowy green rocks.
Eyes are windows into the soul. Shape-shifted creatures generally have the eyes of the original creature, even if they behave differently. Effects that target souls or possess creatures may do strange things to the target creatures' eyes.
Shape-shifting generally mimics the resulting creature, the shape-shifter does not become the target creature. So a shape-shifter may not have all of the abilities of the target.
Vampires aren't actually dead, they have a condition similar to lycanthropy. It's spread by consuming vampire blood. Vampire blood is a sufficiently weak infectious agent that it's unlikely to infect a healthy person, but someone who's had most of its blood drained is another matter. Vampires need the blood of their actual species to heal; other blood simply sustains them. Vampires that have recently fed can usually behave normally, but as their hunger sets in, it takes over their minds. Vampirism subverts its victims minds and biology and is very difficult to heal. Vampires can turn into bat swarms, which can do scary amounts of damage but can't actually drink blood. Vampires sunburn so easily that they take damage from normal sunlight (though racial resistances still apply).
Vampire bites cause lycanthropy. Lycanthrope bites cause vampirism. Too unbalanced?
Taking extra doses of a poison increases the poison's attack or damage against you.
The universe is a pocket dimension. There are various leaks into it; things occasionally get in from outside. Whatever barrier separates this world from outside may be weakening, as it seems that outsider incursions are getting more frequent.
Teleport/plane-shift outside of the world is not possible, unless you can find a leak and teleport from there. That will probably dump you into the astral plane or something.
Weapons made of misletoe always bypass DR. However, it's extremely difficult to make a weapon out of such poor material and they're very fragile.
Inkvine: the sap makes a great tattoo ink, but contact with the skin is excruciatingly painful. In the dragon-lands, slave punishment tattoos are using inked with ink-vine sap. Some slave overseers soak their whips in ink-vine sap in order to make floggings more painful and leave permanent marks without seriously endangering the lives of the slaves. Thanays seem immune to its effects (making it doubly useless on them, since the deep purple of ink-vine sap is nearly invisible on black thanay skin).
One-handed crossbows: very weak draw strength due to being difficult to re-arm. Little damage, short range, useless against armored targets. Bulkier and slower to re-arm than other weapons with similar damage properties (blowguns, thrown darts, etc). Main advantages is that little training is required to use one effectively. Mostly only used for delivering envenomed darts at short range.
Theatrical weapons: Proponents of unusual weapons such as double-swords and blast-staves claim that they make look their wielders look dangerous. Detractors claim that that's only true in the psychiatric sense. People who've tried to use them often claim that they're more dangerous to their wielders than to the enemy. However, generations of warlords and tyrants have sworn by them. While these weapons confer a penalty to hit (even with an appropriate exotic weapon proficiency) and have an expanded fumble range, they provide a bonus to intimidation, which is more useful to most warlords than hit bonus anyway. Theatrical weapons are always masterwork. **Combine this with extremely large weapons, which berserkers can wield with little penalty?
Seven-league boots