Here are some things about the Phantom that could pertain to being part Zelda's moveset:
First off, the detailed design.
I know Toon Link was more detailed in Brawl compared to his games, but the detail was toned down for SSB4.
Here it's like they tried to make the Phantom more detailed in order to fit the Twlight Princess style and match up with TP Zelda more...
Second, the note the color of the Phantom. The only Phantom in the series with that desaturated pink/brown coloration is the Phantom that Zelda controls in Spirit Tracks, and it has the same shield design.
There's a pink Phantom in PT, but it's a more saturated pink, and it has a different shield design.
What does this mean? Well, if the Phantom is an Assist Trophy, then it could be Toon Zelda in the Phantom armor, but that's be a bit unusual.
If it's meant to be a generic Phantom, then wouldn't it make more sense for it to have a different coloration and shield design?
Oh please, it's not THAT long.
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