Clearly, each letter in the word MYSTIFY is moved one step forward to obtain the corresponding letter or the code.
(M → N), (Y → Z), (S → T), (T → U), (I → J), (F → G), (Y → Z)
MYSTIFY → NZTUJGZ
So, in NEMESIS, N will be coded as O, (E as F), (M as N), (E as F), (S as T), (I as J) and (S as T).
Thus the code becomes OFNFTJT.
Hence, the answer is (b).