not too sure about the mander history quest, but i know the second thing is a spell called "black mantle". I do believe you can only learn it if balance is your main school, but there it does have a treasure card.
For the history one, read the quest text. As the text says, enter the chamber of fire, and turn right at the first crossroads. That is, go up on the map. At the end of the path is what looks like a boss area. Go through the door and defeat the boss to get access to the history book.
The -45% accuracy card is Black Mantle, and is given to balance characters for completing the quest The Sixth School, which is just before Ambrose sends you to Krokotopia. Other classes get other cards for that quest, except for Ice, which gets nothing. As it is a balance card, my guess is that other classes do not get it at all.
You have to beat an earlier boss in that instance to open the door to Krokenhamen, before it will show him on the map. After that happens, he wanders around a loop, along with some other mobs. Run around the loop and you'll find him.
Q: Where is Krokenkahmen in the Throne Room of Fire?
yes he is in the hall way (and i find that annoying).
I can't tell you how long I looked for the room he was in...then all of a sudden stumbled over him in the hallway. If they were trying to just change things up a bit while building this area it sure worked!!