The power of the mind and of magic defies your pathetic attempts to understand them, submit and you will be spared
A cold and cadavorous collection of nefarious necromancers.
What if the sources of precious metal in the realm all failed, so that the only sources for gold and other precious metal were hostile foreign lands? Gold coinage might become increasingly rare, resulting in hoarding. Player characters that appear with masses of treasure might be suspected of being in the pay of foreign powers.