The 12 puzzles can each be solved according to standard rules, with the following solutions:
Cave
Nonogram
Tairupeinto
Masyu
Hashi
Number Cross
Slitherlink
Spiral Galaxies
Minesweeper
Kin Kon Kan
Tapa
Thermometers
These are each images from the national side of Euro coins (or, in the case of Sweden, from their own non-Euro currency). The same countries are also each assigned national identification codes for Euro banknotes:
Estonia D France U Sweden K Slovakia E Italy S Ireland T Spain V Slovakia E Austria N Slovakia E Portugal M Greece Y
These letters spell DUKES TV ENEMY, cluing the answer, BOSS HOGG.