????????
      +---------
XTNXM | MYQRUXYG
       -QJUHJ
        =====
         MGRFX
        -QJUHJ
         =====
          LWPLY
         -RYTLT
          =====
          XNJMUG
         -XNFXRP
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: challenging