According to
this, the blue hexagon and the shine hitbox come out on the same frame. So doesn't the fact that we see the blue hexagon mean that the hitbox of the shine is present? And if not, wouldn't that mean that there is technicality a unit of time/input even smaller than a frame?
If you see the blue hexagon come out, the hitbox will appear as well. This occurs when you jump and shine, or just stand and shine.
If you "shine cancel", and the blue hexagon comes out, you are not touching the ground on the first frame of the shine.
Your example in the gif seems to be when the blue hexagon doesn't come out. Here, you only see smoke (if the hitbox DID come out in your gif, then you missed mario with it).
For whatever reason, if you are moving on the ground (which implies touching the ground, obviously) on the first frame the shine comes out, the hitbox will not appear, but the smoke will.
Why? I'll wager a guess: It's probably due to the programming order (i.e. sequence of events).
It's probably something like...
...if down+b is inputted, then:
1. smoke animation appears (stuff could occur before, like the shine sound)
2. is fox on the ground? y/n
a. yes (go to 3)
b. no -> ok, hitbox can appear as well (i.e. air shine)
3. is fox moving? y/n
a. yes -> hitbox will not appear (this is likely because the game programmers decided that if fox is moving on the ground, then the hitbox won't appear -- this makes intuitive sense to me, otherwise you could run around and shine cancel with hitboxes coming out LOL)
b.. no -> hitbox will appear (i.e. a standing shine, lol).
If you're moving horizontally across a perfectly horizontal platform (e.g. Hyrule middle platform), and shine, you are seeing 2b above (where the blue octagon appears, and the hitbox comes out).
If you're moving horizontally across an upwards slope (and are holding a down-diagonal direction so that you stay on the ground), and shine, you are seeing 3a above.
Another interesting case of 3a is the "perfect-shine" off the respawn platform: Here, it's 3a because fox is programmed to drop on the same frame you shined. This is moving, but not because you inputted a direction.
...An interesting question cuz it forces you to think about chronological sequence of events (there was a thread that showed this for all moves).