Nice! Although, I think a number of these assignments are up for debate, namely Mac having his own tier. Sure, he's bad, but I wouldn't say someone like Plant is a whole tier above him.
Ridley certainly isn't good, but he's probably not bottom five. His kit has no real synergy or cohesiveness. He's effectively a bait-and-punish character who can't bait, and gets less reward from a punish than other characters. He's combo food without the survivability of a big character. But, in spite of all of this, he's got a fair neutral and good advantage state, with enough killpower to be a threat. Though on paper he doesn't do much very well, we've seen people like Trela achieve legitimate success with him, and I think his results warrant at least a C-tier placing.
Greninja, for that matter, probably shouldn't be in C-tier. He has a place in the metagame, even at the highest levels of competition; many players, especially Japanese ones, consider him to be high or even top tier.
Shiek is someone I actually agree with not being bottom tier, but she doesn't have the results to justify an A-tier placing. She's got everything a character needs to be competitive, but the lack of damage and killpower are severe. I maintain that a character with her frame data, neutral, combo game, advantage and disadvantage state cannot be low-tier, but I can't confidently call her high-tier, either.
Aside from that, some characters like IC's, Puff, Pac-Man, K. Rool or Ganon probably don't belong where they're listed. Generally, though, I don't think the game is old enough for many of these things to be set in stone, so viability can still be up in the air for a lot of fighters.