Oh hey this video is actually super good.
For clarification of the forward smash and some sort of power-up, I firmly believe one of two things:
A) The more likely one, the zoom-in is because the hero is under the influence of "Psyche Up". I mostly believe this because if you listen carefully to the sound of the forward smash hitting, it makes the critical hit sound effect which is also heard on hard hitting Psyche Up hits in the original games:
Critical Hit sound (old retro one):
https://www.youtube.com/watch?v=i6zl-Y6R8Vg
Smash trailer (listen carefully around 1:33 to the sword hitting, playback speed 0.75 helps):
https://www.youtube.com/watch?v=pupll3ON-WA
Psyche Up hit in Dragon Quest 8 (around 0:40. While these sound effects all vary slightly, they are all clearly critical hit sound effects imo):
https://www.youtube.com/watch?v=VOldiyyYEkM
B) My second theory is that Hero has some sort of Critical Hit effect on his sword, perhaps being the tipper. I don't personally believe this since psych up exists and also uses the same sound effect when hitting a powerful move, but it might be worth considering as a backup theory.