????????
      +---------
QLNNM | PNFRFQYL
       -QLNNM
        =====
        RPLQHQ
       -RQGFYG
        ======
          NHPLY
         -MYGGR
          =====
          RPLEXL
         -RQGFYG
          ======
          ??????

base: 13
letters: EFGHLMNPQRUXY
difficulty: challenging
missing: U