This hint has really got me stumped pretty well. Its very unclear about what it means when it references the character using a single special attack on the ground. Does it mean that their Jabs, Tilts, and Smashes are worthless? Does it just mean that they are best used by spamming that B attack on the ground? There is so much variation produced by just that one line that it makes this one far too variable since we dont know exactly what traits that line actually hints at.
However since there really isnt a character that is best off on the ground only using 1 B attack instead of other attacks (though not necessarily specials) I think that it doesnt mean their other ground moves are bad at all, but that they will rely rather HEAVILY on a single special attack while on the ground. Since pretty much every character has either a good tilt, jab, or smash use alongside their special attacks when grounded.
So what we need to look for are probably characters with no more than 3 or 4 good ground moves, and one B attack that pretty much dominates their ground game. Also we need someone with relatively poor recovery in terms of it being able to be gimped, but it also cant be total crap either, otherwise gimping isnt necessary and thus fighting a skilled or unskilled player wont change their chance much to recover. And yeah, they need a *surprisingly* good aerial game.
Ganondorf fits fairly well, but his recovery is pretty hard to gimp, poor as it may be. The skill of an opponent isnt going to turn gimping him into an easy task.
Peach fits pretty well too. Even though her f-air isnt as great as it was in Melee, its still quite strong, and her n-air is still great as well as u-air. On the ground she relies a lot on turnips, lacking useful tilts due to range issues. She also has a decent recovery, but its definitely gimpable if you know what you are doing.
Wario also fits quite well. Knocking him off his bike as he tries to recover isnt that difficult, you just have to avoid or outprioritize the bike hitbox and be able to hit Wario as well with any aerial with half decent knockback. He really only has one good ground B move that you want to use with any frequency, but I wouldnt really say it dominates his ground play.
Yeah...this hint really sucks...too vague, it leaves too much of what the hint actually means up to those solving it (so its sort of incomplete), it doesnt fit any character well enough.
Plus I dont even think that any of the characters Im coming up with are even worthy of the 8th best in Brawl title.
Thinking about it though, I believe we should work at this hint from the recovery aspect first, then we need to look for a character with a strong aerial game, and from that list use the special attack hint to narrow down the list. If we try it in any order the use of the hint in solving it becomes too subjective, since the person must interpret the hint itself a great deal when it comes to that part.
. Maybe it will be meta knight or rob as well. Maybe snake too. 
