Marth, Lucina, Pits and Meta Knight all have sword trails that start the frame before the hitbox.
In some of meta knight's cases it's to cover the fact that he only has really short durations (HIS UP AIR IS ONE FRAME) and that the hitbox travels between two points within that single frame; so in MK's case here it kinda makes sense - there is still hitboxes appearing around these slashes.
However in Marth's case, it's particularly awful, none of these moving hitboxes; we're not pushing 4 frames of hitboxes into 3 but giving 4 frames of visuals, we're just removing an entire area where people would expect hitboxes to exist.
Meh.
In some of meta knight's cases it's to cover the fact that he only has really short durations (HIS UP AIR IS ONE FRAME) and that the hitbox travels between two points within that single frame; so in MK's case here it kinda makes sense - there is still hitboxes appearing around these slashes.
However in Marth's case, it's particularly awful, none of these moving hitboxes; we're not pushing 4 frames of hitboxes into 3 but giving 4 frames of visuals, we're just removing an entire area where people would expect hitboxes to exist.
Meh.