Running shine

You can shine while running. Not only does this mean that a running Fox is permanently threatening a frame-1 hitbox, but that hitbox also leads into all of his shine combos and some extra ones enabled by the momentum of a running start.

While not a hard requirement, the true power of running shine is unlocked by the ability to Waveshine. This will let you convert the shine into a grab, up smash, or aerial-based punish on sliding characters or into a down tilt, up smash, or Thunderz' combo on others.

For these reasons, running shine is probably the best whiff-punish option in the game.