As playable character, 0.5%. As a Pokemon found in Pokeball items, 25%.
Nominate Alice (Balloon Kid) x5.
And by the way, I believe significence and how successful the titles the characters appeared in sold are sometimes more important than popularity. Even though, EarthBound wasn't successful in America, but MOTHER 2, the Super Famicom version, was successful in Japan. I believe that successfully-sold, Japanese versions have a better chance at having their representatives in SSBB, than the successfully-sold, American versions, because Nintendo is a Japanese company. For example, Fire Emblem 7 didn't sell in Japan as successful as it did in America. They added Marth, not only because he is the very first Lord of the Fire Emblem series, but his most recent Fire Emblem appearance, Fire Emblem 3, is the most successful Fire Emblem title. I heard there were over 800,000 official copies of it sold in Japan. I know Fire Emblem 6, Roy's first Fire Emblem appearence, didn't sell too well, but Roy was added to help advertise it. Also, Sakurai was running out of developing time, and decided to add some clones to spend less time and effort. I'm pretty sure Roy won't appear in SSBB. Even though, he is interesting. Am I correct on all of this?