????????
      +---------
MRNRM | FLLQEUUL
       -MRNRM
        =====
        NRGUMU
       - MRNRM
        ======
         WNHWJU
        -EUGMUH
         ======
          WGFLNL
         -EUGMUH
          ======
          ??????

base: 13
letters: EFGHJLMNQRUWX
difficulty: hard
missing: X