Slight bug:
You can't start a match with Neutral B, he doesn't turn invisible.

Also his Aerial Down-B is easily interrupted, in my experience.  A dash of wind knockback, perhaps?

@Dotz:
If I worked on something for hours, maybe even days, and all I got in return was a bunch of rude comments and "meh" I'd be pretty upset as well.  ;p
A lot of people around here seem very edgy and standoff-ish, it's probably best not to contribute toward that atmosphere, right?
Just sayin'~

@Dotz:
I highly doubt he made this PSA for the sole purpose of originality or satisfaction of the people that browse this forum.  He made it because he thought it would be a cool idea (an assassin), and his idea best fits on Marth.  Also your feedback has almost nothing to do with his PSA at all, aside from the idea that it's "not original."
Originality has nothing to do with whether or not PSA is good, nor does it contribute constructive feedback.
If you want something original, do it yourself, because I doubt this was his goal.
As far as I'm concerned, PSAs provide nothing more than satisfaction for the creator and possibly a few of his or her friends, not to swap out the entire roster based on what other people demand.

Keep in mind I'm not trying to be derogative toward you, I'm just giving you something to think about.
Consider what the creator's goal was rather than what you wanted out of it.

[Grounded Down-B]

This PSA is pretty neato, I do have a few suggestions though.  (Played on Brawl+)
•Grounded Down-B:  This move is ridiculously good if you can use it well, great combo ender and pushes you well out of the way to prevent most punishment.  I suggest a whiff animation if he misses the attack, allowing it to be countered.  Or reduce the damage on it, 19% is a bit much.
•Up-Tilt: Neato, but seems out of place.  Could use a hitbox near the beginning of the animation.
•Aerial Side B: Simply feels like it should do something.  Possibly make it cancellable with Aerial Down-B?  Or make a strike at the end of the dash that ends with helpless falling.
•Down-Tilt: Seems a tad out of place, hitbox is weird as well.

Also a general suggestion, I think you're underestimating the power of Neutral-B, in the right hands this could rock people left and right.  You may need to compensate for this by making him lighter or weaker in general.  Fighting a ghost isn't an easy thing to do.  I also had a thought where you could have a subtle smoke effect during the vanished phase, but that kinda ruins the point.

Aside from the aforementioned, I'm loving this PSA.  It doesn't seem ridiculously overpowered or over-the-top.  It almost feels like he belongs in this game, which is what people should be aiming for.
Keep up the great work, and I'm looking forward to your future projects.