A drunken POM, MARK, and a FINn.
A SASHIMI FISH bar they broke in.
Stole many a dish,
Ate FILLET-O-FISH.
Now CHAINed in a CELL those Gaijin.
POM=An acronym used for Pattern Overlay Method
MARK=An alias used for pencilmark. Also the act of placing them in the grid
FIN=The additional candidate(s) in the box constraint that belongs to a Finned Fish
SASHIMI FISH=A variety of fish where not all defining candidates are present
FILLET-O-FISH=A variety of fish that uses an additional box constraint
CHAIN=A series of linked cells or candidates
CELL=A small square in a Sudoku grid that can contain a single digit
POM=Ozzie term for a Brit
FINn=Someone from Finland
Gaijin=A non-Japanese person in Japan