Mass09's Ledger really is one of the most interesting and underused items that can be found in vanilla subdungeon.
To get a grasp of all it's possible use cases it can have, you should look at this gem from the game's wiki:
http://www.qcfdesign.com/wiki/DesktopDu ... s09_LedgerWhile it's generally as not worthwhile as the usual vicious reward items, it certainly is quite useful and fun to play with.
I added it to my locker recently because I have finally reached golden borders on my Hard dungeons and will have to do a bunch of GoatPerson runs, and I believe that it will be extremely valuable.
I am equally convinced that it might be possible to leverage it in FFFF pt.3 (but maybe not, 18% resistance is quite a lot there).
For now I didn't use it much, but I took it for a spin in Ick Swamp and it was really funny to get rid of all the plants using it (even though I cheated, that was a Crusader Hoarder PQI).
It can be reaaaally nice in Cursed Oasis or Creeplight Ruins, anything with Shades, really.
We made an expansion and it is awesome. Really, you should check it out, especially if you're looking for some extra challenge.
Download over at ddmod.weebly.com!