MWG
      +--------
FPGGU | JXMNLTY
       -FPGGU
        =====
        NTNUGT
       -NNFQRU
        ======
         URFMYY
        -UXMNPH
         ======
          NYGFY

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard
missing: W