New update... but see disclaimer at the bottom.
The purpose of this update was to get the secrets working, and yes, they are certainly working. Two new races have been added as secret-keepers: Shamans and Star Sprites. Both are reclusive races who live mainly in caves, although you'll occasionally come across a city-dwelling Shaman. Both have some very unusual properties:
Shamans are born with the ability to cast powerful lightning and ice spells, and are naturally resistant to heat and cold attacks, though they tend to be physically fragile. They can also improve their odds of victory by placing curses on their enemies (much like a mummy's curse, but temporary) and charms on themselves or their allies (which has the opposite affect). They make excellent allies, though adventuring alone as one may be a bit of a challenge due to their delicacy.
Star Sprites are weak on their own, but they have the ability to give their allies the ability to perform support techniques on them by wishing. Wishing on a Star Sprite greatly increases all of its physical stats, and if a Star Sprite falls in battle, it can be wished back to life as long as its allies are still standing. You can't play as one, but if you're lucky enough to get one as an ally, it will serve you well.
As for the secrets themselves: Teleportation and Polymorphing have been merged into a new secret, Magic, which gets a damaging spell as well. Polymorphing has been changed; it is now a single attack that has one of several effects. It has a small chance of transforming the victim into a mushroom (which is basically game over), but will usually trap them in an egg for a short time instead. When the egg hatches, there is a reasonable chance of coming out as a random creature, generally of the small and weak variety, although if you're lucky, you might turn into a Toad, Koopa, or even a Yoshi. If you're really unlucky, you might hatch as a Cheep Cheep instead.
Firebrand and Thunderhand have been improved somewhat: Firebrand gains a 'Fire Finale' attack which gives you a short period of time to basically crispy-fry everything in the immediate area (but can only be used once in a decent amount of time), and Thunderhand users can now electrically charge their allies, granting them a short-range electrical attack as well. In addition, several creatures have been given a weakness to electric attacks, including Chomps, Belomes, and Smithy Units in tank form. Also Metal Elementals, which is now a new creature, by the way (you can become one through a 'curse').
Speaking of which, becoming a Tanooki or a giant is now considered curse. And in homage to their original appearance, people can acquire the Thunderhand and Firebrand techniques by defiling temples as well. I think some sacrilege is in order.
People weren't dying enough in worldgen, so I added two new megabeasts: Fryguys and Dragons. Mushroom World dragons are quite different from vanilla DF dragons - they can only breathe regular fire, but are quite durable and hard to make bleed. They also have a surprise in store for anyone who tries to get rid of them by trapping them in a magma pit. In homage to the Czar Dragon, Bonetail, and Bone Dragons, larger dragons (a bit larger than around half the size of an elephant, which should start appearing in worldgen at around the year 100) can survive having their flesh boiled away, and will emerge from the magma as a fierce skeletal dragon that can no longer breathe fire, but will no longer bleed or feel pain; the only way to kill one is by removing the head or destroying the brain.
Now for the disclaimer: I am not sure that this version actually works. I've been seeing bugs that make no sense at all, random crashes when loading the raws for any purpose, but only sometimes, and if you return to the menu screen it always happens if you try a new mode without exiting, also there have been weird characters showing up in place of the regular non-alphanumeric characters... Oh, and intangible creatures have joined the impossibly hard ones, and I didn't put any Metal or Vanish caps into the game (if only there was a way to harness these bugs!). The raws all check out and there is nothing in the errorlog, so I'm assuming that this is just some bizarre effect specific to my computer, but I'd like some confirmation from testers that it actually works properly on other computers. On that note, has anyone else ever encountered the unbreakable bandits that I've mentioned in the bugs?
Have fun, and let me know if this thing works please!