I see I left an impression with the dropping a weight class idea XD. Luckily I was ready for you, Storm, since I did some research and have about 20+ move-set ideas.
Darkwing Duck (Taunts: Down = Stares at the screen and you hear "Let's Get Dangerous" in the background, Side = Takes his magnifying glass and starts to walk a little as if looking for a clue, and Up = Purple smoke encircles him and when it clears you see him holding his cape out like wings. In the background you hear, "I am the terror that flaps in the night, I am the water balloon that lives right on your head, I am DARK WING DUCK!" (the second line is always different, but that's the one I liked the best))
B: Shoots his gas gun releasing tear gas. The shell releases the gas when it hits the nearest object (ground, character, etc.) doing 3% damage for every 0.5 seconds it hits a character. The gas continues to release for 2 seconds.
Side B: Darkwing Duck uses his gas gun to have a boxing glove shoot out. This attack has a range of Pikachu's Side A, does 12% damage, and has decent kick-back. If it hits, the background sound is "POW!"
Down B: Darkwing Duck has a small smokescreen (thick) appear at his feet due to him shooting it out of his gas gun. When the smoke covers him he then shoots out another grenade, which is filled with laughing gas, if it hits the opponent it does 8% damage. The attack takes about 1.5 seconds to do and, if successfully hits, causes the opponent to move in a stupor (like a shield breaking) for 1.2 seconds.
Up B: Shoots his grappling out causing it to wrap around the legs of any character it hits. When it hits it causes 1 second stun and slams the opponent on the floor (like when you dodge and lay on the floor and have to press up to recover). This attack does 8% damage and has a range about the same as Olimar's Side A. This attack can be used to grab on to a ledge.
A: Darkwing Duck does a left-handed karate chop and then follows up with a punch from the opposite hand. Each attack is separate meaning you have to press the A button twice to activate them at the same time (alternates). The karate chop causes 0.25 seconds of stun and 5% damage, while the punch does 12% damage and decent kick-back (non-charged). If charged, the karate chop does 0.5 seconds stun and 8% damage, while the punch does 19% damage and major kick-back.
Side A: Darkwing Duck kicks out at the opponent with one, major, kick; this attacks does 8% damage (non-charged). If charged, the attack still does 8% damage, but Darkwing Duck follows up by shooting out his grappling hook. The grappling hook shoots out at the person and if it hits the person, does 4% more damage and good kick-back.
Down A: Darkwing Duck spins around in a circle, hitting anyone near with his feet; this attack has the range of Pikachu's Down A and does 7% damage (non-charged). If the attack is fully charged it does 11% damage and twice as much kick-back (average).
Up A: Darkwing Duck takes out his gas gun and shoots up an explosive bomb into the air. It's kind of like Snake's mortar, but you can choose when to blow it up by pressing the grab button (like Snake's rocket launcher). If non-charged, the bomb falls slowly and does 7% damage and 0.75 seconds of stun. If fully charged, the bomb does 12% damage and a full 2 seconds of stun; the bombs fall speed is greatly increased.
Final Smash: Purple smoke fills the entire screen and you see a close-up of Darkwing Duck's face; he then says, "Let's get dangerous." Darkwing Duck then turns into "Dark Warrior Duck" and gets a new costume and weapons. A tank appears on one side of the screen and lets off a shot that kills anyone that is hit (small size, long range). The tank then disappears, but is replaced by Dark Warrior Duck's flying robots who home after the nearest player and attack them until they die (or time runs out). Dark Warrior Duck goes up to the highest weight class and takes damage at 1/2 of what he normally does and 1/4 of the kick-back. His gas gun is now a mini missile launcher and he can shoot them out by pressing B. This Final Smash only lasts for 10 seconds, so while deadly... it's short.
Darkwing Duck was a NES game, made by Capcom in 1992, so I'm sure Nintendo would be able to get the rights for him. After all, the show only aired for one year.