Sakurai's an artist, I'm an artist, and for the sake of this argument, let's say you're an artist too. I love your work by the way.
We've been tasked to design an eclectic and exciting cast of characters. Let's start with basic sketches, no colors yet.
Draw Marth. Now draw Lucina. Inspired by the original, slender, long hair, different costume but with allusions to her predecessor. A good pair.
Draw Link. Now Draw Toon Link. He's a different take on the original, but goofy and youthful. He isn't meant to be as serious, but still just as fun. Give him some cat eyes.
Draw Zelda. Now draw Sheik. We know it's the same girl, but the design doesn't scream that. There's a different stance and attitude to her.
Draw Mario. Now draw Paper Mario. Similar to the Link/Toon Link deal. One's a simpler, goofy, alternate version with an arsenal of accesories that make him stand out from the original. Now draw Dr. Mario. Okay, so you just put a coat on Mario. Scratch that.
Draw Fox. Now draw Falco. Haha. Sweet.
Now Draw Pit. And then Dark Pit. You know you're drawing the same character over and over again, right?
Fine, just color them, we'll make it a palette swap.
Also, Don't Google Pit/Dark Pit. Eww.