3 (4 potentially) characters for a series isn't too much at all. Leon has interesting potential. First off he's an assassin so we can probably get away with using poison themed moves. And he's a chameleon so deception/being methodical can be part of his moveset (If you're wondering how any of these have anything to do with being a chameleon, they change colors and hide so deception is pretty obvious, being methodical comes from the way they move, watch a chameleon walk around some time, they always shake when they move to make themselves look like leaves, and they're very picky with the direction they go in.) Based on his N64 personality he's arrogant but composed/patient. Combine all aspects of his character and you can get a character that plays methodically by racking up percent with poison-esque moves and then comes in for the kill with safe finishers. Balance him out by making him slower and floatier than the other spacies with a couple of kill moves with rest for used for creating space.
Here's some ideas for his special moves. I'm not too imaginative so if it's a bad idea I apologize in advance.
His blaster does low/no damage when it hits but will add damage over a couple of seconds with no knockback/hitstun. Maybe give his blaster a hitbox like Wolf that stuns/sleeps after a certain percent. When used from the air it can be angled down to work with his reflector. Basically a poison themed blaster shot.
His reflector will be tossed away from his like Falco's, it will deal moderate damage and trip the opponent. If the opponent is within "shine" range they'll be pushed in the direction that Leon is facing.
His flash will be horizontal, it will knock opponents in the direction of the flash if not sweet spotted. If sweet spotted he will grab the opponent, and have a 1 second window to throw, if not thrown he will poison the opponent and spring himself away. If grabbed in the air he will just spring away.
His Up B will have the same knock back properties as Firefox but will be poison themed, low initial damage with a DoT component.