Battles take up SO much time in this game. It's in our best interest as speedrunners to skip as many battles as possible. Thankfully there's two super-useful books that can let us do just that: the Bluff Guide and the Corruption Guide.
The Bluff Guide lets you skip any non-boss fight with sentient enemies (everything that's not a wolf or bear) for FREE. The book isn't even consumed! You just get to skip pretty much everything! This includes random encounters you get from searching buildings. Amazing.
The Corruption Guide lets you skip any non-boss fight (including wolves and bears) for 1gp. Further, if you borrowed money from the Banker, you can give him the book at the end of the run to skip having to pay him back or fight. Wicked.
Now I hear you asking, "Where can I find such amazing books?!"
The answer is, "A lot of places very very randomly, and a few places less randomly."
The most "consistent" way to get these books is actually through a character-specific reaction for Erus. There is one event you can get that talks about finding a cool library and if you search it, you just get a regular book. However, if you have Erus in your party he finds you the Bluff Guide AND the Corruption Guide AND the Reseller's Guide! Holy wow!
Now you might be thinking that such an event is hard to find or perhaps the result of a rare building. Nope! It actually has a chance of happening on any "middle-class homestead". In the City, this means "Houses" and everywhere else it means "Cottages", but not the ruined ones, the nice ones. I have not seen this event pop up in the Necropolis although if I had to place a bet I would say you could probably find it in the Mansion.
In any given run, you're bound to find at least 2-3 eligible locations PER MAP. It's not guaranteed that you'll get this event, but with the sheer volume of them, it's not uncommon to find it. Speedrun-wise, it's all about finding these books as quickly as possible so you can stop wasting time with encounters and blast through the game.
OTHER LOCATIONS THAT CAN DROP THE BOOKS Castle Loot The Gypsy The Thief Master Any other event that grants a random rare item
