MFFN
      +---------
JTXEP | PEMQFJEF
       -JTXEP
        =====
        MUPQGJ
       -MXHJHG
        ======
         MUNRXE
        -MXHJHG
         ======
          MJXHMF
         -MTXHGJ
          ======
           TEETE

base: 13
letters: EFGHJMNPQRTUX
difficulty: hard