Tutorial: Editing Compressed Graphics

Are they compressed or in some specific format?

The monster graphics are located from E97000 to ECE3BF, but they're diced and mapped tiles.  Not exactly compressed, but not in a format that is easily or comfortably edited in YY-CHR.

You'll probably want to use FF3SE (A graphics editor designed to handle both the tiles and the pointers)
https://www.ff6hacking.com/wiki/doku.php...util:ff3se

Or you can use Madsiur's branch of that same utility if you intend to expand the monster graphics (though I'm unfamiliar with the differences as I have not used this version)
https://www.ff6hacking.com/wiki/doku.php...l:ff3semod

EDIT: Ninja'd.