FLXX
      +---------
UNLFT | UYGMGPYU
       -UNLFT
        =====
         JMHNP
        -TQXLY
         =====
          PXULY
         -WNHNM
          =====
           WMYUU
          -WNHNM
           =====
            XUYM

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: medium
missing: R