It's sad that this is the final tier list for brawl because a couple characters with lots of potential, Fox and Sheik, were extremely underdeveloped since they, mostly in theory, had some very difficult match ups. Fox had incredible speed, dangerous punishes, high kill power, and could quickly inflict a lot of damage. Despite having these really good traits, he, like Sheik, was one of the more difficult characters to use and was rarely represented in top level play. We don't even know if his match ups against the characters that could infinite him were really that bad in practice. I think Fox could have possibly been in the A- tier with Marth, Falco, and Snake.
Sheik had a quick-all use projectile, an extremely quick moveset that gave her an excellent punishing game, one of the best combo abilities in the game that allowed her to get her opponents to kill % in a short amount of time, as well as a long reaching DACUS and some decent edge guard tools. Her weaknesses included having a poor recovery, lacking good landing options, the combination of being a tall-fast falling-lightweight, as well as having below average kill power. Even though Sheik did have some high level representation thanks to players like Ed and Cross, there weren't enough top players who explored her and tried to improve her poor match ups. I think Sheik could have been in the C tier.