Mysterious Journal is a Quest book found during the quest: 
Up in the Air.
(Most of the pages seem to be damaged by wind and talons, but there are a few entried that remain legible, written in an elegant cursive hand.)
- Runestones, Fly (30) Spent
- Runestones, Barrier (5)
- Potion, Charm (2) Lost
- Potion, Fire Resistance (2) Lost
- Rations, Three Days
- Change of clothes, Three Days
He's right, if there is a cure the Humans will know of it. They've locked most of their knowledge away behind these ridiculous puzzles. Some of the new Humans have begun to uncover their secrets. I must get there first, or risk discovery.
(The rest of the page is smudged by the elements.)
(This page appears to be mostly waterlogged, save for a few sentences you can make out.)
...The Temple of the Waves has a quiet beauty to it that reminds me of the Bay at dusk. If I were not in such a rush, I would stay and see what secrets still remain locked away...
(Soot and burns cover most of this page, but you make out what you can.)
...Temple can fall to the Pyroflow it houses for all I care... heat's made my foundation run right off my face... blasted Kitsuu...
There is someone on my trail. I can feel them getting closer. Will need to rush the Gales.
(The next words cover half the page, in heavy bold:)
FORTY EGGS?!?!
(The rest of the journal is blank.)
This article or following section is likely to contain spoilers! Please proceed with caution.Mysterious Journal can be found in the Temple of the Gales during the quest Up in the Air. It is found within the temple that houses the four eggs. Once inside, head up the stairs; there will be a Mysterious Pack laying on the ground. Once the pack is opened, the Mysterious Journal will appear in the quest items tab of the player's inventory.
