Black Shadow + Fawful joining would be a pleasant surpirse. Besides, I have a theory that black shadow was supposed to be in melee.
Take a look at the roster below, notice anything out of place?
Every single series has all the playable characters lined up in a row, except the Zelda series. Ganondorf just happens to be a clone of Captain Falcon and has dark looking moves that easily could've been a black shadow moveset. I think that nearing the last few days before they released melee, they realized that the game had 1 villan (bowser) and decided to put in another. The team came up with Ganondorf, Dedede, and Black Shadow, and Black Shadow won the vote because they already had 3 other Zelda reps at that point. Dedede was canned one again due to there being too little time to develop another full moveset. Somewhere along the line, someone must've said that the Zelda franchise was better selling, and Ganondorf was more recognizable by people so they just reskined Black Shadow with Ganondorfs model, and never bothered to change his position on the roster.
Furthermore all clones in melee, are clones of someone else in there respective series.
Pichu = Pikachu
Roy = Marth
Luigi + Dr. Mario = Mario (If you would even call Luigi a clone)
Falco = Fox
Young Link = Link
Ganondorf is the only exception to this, being a clone of Captain Falcon, who is from another series.
This is just a theory however, so don't take it to heart.