Why do the Setites have their hands on anything that ever happened? The inquisition, the Anarch revolt, the fall of Rome, The sacking of Byzantine, the enlightenment, and the French revolution. Just to name a few of the things they're apparently secretly behind. Hell, they're partly responsible for an entire other game line. (Mummy)
Don't forget Werewolf, where Sutekh screwed over both the Silent Striders and the Bubasti werecats, both tribes with bloodline curses that still hold strong to this day. And no, the books never explain how Sutekh pulled that kind of power out of his ass.
Set is one of the Vampire's setting's big-time Villain Sues, along with Tzimisce and Saulot.
Did White Wolf ever describe what would happen if a vampire managed to embrace a werewolf or changeling (assuming the werewolf doesn't rip the vampire into shreds)?
Old World of Darkness, later editions? The werewolf usually dies. Sometimes they survive to become an abomination, but since the Sam Haight fiasco, those are all fated to become ashtrays, and very rare to start with (there are about two other abominations in canon and at least one is heavily suicidal, being kept out of the sun only through mind control by uber-elders). Changelings go insane and have their fairy soul go permanently pop, so they just become crazy vampires (or in the case of Malkavians, crazier vampires).
It varied depending on the target. Most shapechangers would either die or rarely become Abominations. An Embraced Kitsune (werefox) immediately goes up in a pillar of fire, taking the vampire with it. Nuwisha (werecoyotes) die immediately if a vampire tries to embrace them. Embraced Ratkin (wererats) decompose until their bodies can no longer function. Corax and Mokole (ravens and reptiles) had it worst; since they were both tied to the Sun, they would die by the next sunrise. Corax generally just spiralled into dperession; Mokole spent their last night in a permanent, mindless frenzy. Bastet (werecat) abominations bleed Gnosis constantly until they have none left.
In New World of Darkness, werewolves and changelings are immune to embrace or it replaces their existing template, depending on situation and GM fiat. Werewolf blood tends to drive a Vampire into Frenzy, and Mage blood gives them hallucinations. Assuming they got past that, more likely than not the target would just die. Mage souls are tied to their respective Watchtowers on the Supernal Realm, so the Embrace probably wouldn't take for that reason (but that's just Wild Mass Guessing).
Actually, there is one instance where a werewolf might be Embraced in the nWoD, and that is the Dead Wolves bloodline from Shadows of Mexico. Dead Wolves have access to Totems and Fetishes, and they have Auspices, so it's about as close to an Embraced werewolf as is possible.
What happens when a vampire tries to feed on a Promethean? I presume Hilarity Ensues. And does Genius blood make them smarter?
It's explained as "tasting like dust". Promethean blood is, essentially, just for show or until something real is replaced.
I found the rules, Promethean blood is half as good as human blood and probably not nearly as tasty.
According to the Genius book, for vampires Genius blood is no different from ordinary blood, with no bonuses or penalties. (Check page 360.)
Is there ever a slightest glimmer of hope, or one happy ending just so I can smile at the end of a session.
Only if you convince your ST beforehand to let you Earn Your Happy Ending. Alternately, release your inner hog and start forcibly (but smartly/cautiously) pushing things in the "worse" direction so that you increase the crapsack quotient. I have this theory that the WoD (and a few story tellers) aren't so much "pro-crapsack world" as they are "anti-let the PC's change things". So if you actively work to destroy things, they'll start getting better! ... and if I'm wrong, then at least you'll have at least succeeded at kicking the dog to boast about.
There's technically nothing that says you can't make a slow-but-steady improvement in your game, or even achieve a happy ending. Granted, it won't last too long unless it's an endgame scenario, but it's doable. If your Storyteller isn't too high on the power of being such, he/she should let you achieve your goals so long as they aren't improbable (i.e., 'rescue my ghouled relative' is doable, 'create world peace by eliminating all supernaturals' is best reserved for an end-of-days event).All gamelines have something you can latch onto to create a lighter or happier resolution: Vampires have their Humanity (especially the younger ones), Changelings can successfully inspire Dreamers to better things, Mages can make headway against their enemies or even team up with them against Nephandi, Horrors from Beyond, ect; Hunters can see that their little part of the world is safe, and even start working together as part of a larger Hunter group to start clearing a city, county, or even just making positive ties with other supernaturals. The World of Darkness should live up to its name, but there's absolutely no reason your PCs can't be glimmers of light.
Does NO ONE in the World of Darkness own a dictionary? I remember quite a few where it was just obvious what the big meta-twist was going to be, but the one that floored me was Autocthonia. Really. Go look it up.
I always get confused because in French 'autochthones' means 'natives' (as in Native Americans). I'm not seeing any English-language definition that seems particularly evocative of what Autochtonia is in Wo D. Although to speak about evocative names generally, this is particularly odd, since the people who discover things or the people who talk about those things often are generally the ones who name it and they wouldn't have any meta-knowledge about the objects.