  We reduce the termination of flips to the termination of terminal flips and
the ACC conjecture for minimal log discrepancies (mlds) for exceptionally
non-canonical (enc) pairs, a class of very restrictive singularities. As a
consequence, the ACC conjecture for enc pairs implies the termination of flips
in dimension $4$.
  We also show that the termination of flips follows from the
lower-semicontinuity for mlds for terminal pairs, and the ACC for mlds for
terminal and enc pairs. Moreover, in dimension $3$, we give a rough
classification of enc singularities, and prove the ACC for mlds for enc pairs.
These two results provide a proof on the termination of flips in dimension $3$
which does not rely on any difficulty function.
