I cleared 9.9 as Roy, G&W, Snake, K. Rool, Captain Falcon, and Little Mac. I think the key is getting KO's fast. Most of those were on stages that you can walk off, so all you have to do is hit them to the edge and then throw them off, it takes like, five seconds. Then it gives you a higher intensity, and you hit 9.9 before the boss. (Which is key, considering how hard it is at higher percentages. I found out that if you haven't hit 9.9 before the boss and the boss KO's you, it's impossible to hit 9.9. It won't take you to 9.9 even if you're at 9.8!) I only play as Snake a lot in that group and surprised myself with all those 9.9's.