IMO I think Mewtwo's bad but not bottom of the barrel. I'd put him mid-high of the lower tiers.
This is my opinion on the "bottom tier" based on no customs:
Charizard is definitely underrated. I'm like 100% biased but I think Charizard is underrated (i has teh lizardon flair). Tons of reliable killing options, fantastic recovery, super armor, above average dash speed, fantastic grab and throws, etc. Thing that irks me the most is his aerial movement. Everything else is pretty great. Don't understand why some consider him as the worst character in the game not counting Swordfighter... I honestly think he's one of the better heavies. Better than Dedede, DK (w/o customs) , and Ganon (w/o customs) at the very least. Middle-high of bottom tier.
Falco is underrated. He's super nerfed but I honestly think he's still pretty great. His grab and throws are pretty darn good... d-throw and u-throw combo into a lot of things. His recovery is pretty good as well. Uair and bair are amazing. Bair especially, jesus christ that move is so good. His tilts are also really good for spacing. Just a fantastic character overall imo... I don't really understand why some put him bottom 5... if anything, I think he's near the top at the bottom tier (D rank?). He has a lot of flaws (fair, dair, and laz0r sucking, he's uber slow, easy to combo, etc) but I honestly think he's a lot better than most of the bottom tiers.
Meta Knight is underrated. God-tier recovery, and TONS of combos. More than some of the top tiers, even. This guy is god at gimping if you do it correctly. One of the best recoveries in the entire game. Decent killing moves, although they are risky. Biggest flaw is definitely his range. I really don't consider this guy bottom tier... at the very least, bottom of mid tier. The most recent Japanese tier list put him mid-high which is pretty close to what I think his tier placement should be. He's definitely not bottom 10.
Kirby and Robin are also underrated. Won't elaborate too much on this because I don't play them much, but based on what I know about these characters they're pretty darn solid. Kirby has mad combos and Robin has a great zoning and projectile game. I honestly don't think Robin is bottom tier... mid-bottom at the very least.
Ganon is overrated. He's extremely fun to play and to style with but he's overrated. Terrible approach options, terrible recovery, extremely darn slow, etc. The top tiers can just camp him and he can't do anything about it. Extremely vulnerable to gimps as well. I don't agree with most people considering him as mid-bottom/top of the bottom. I love Ganon and he's super fun to play (he's in my top 8 in my fighter records) but I honestly think he's bottom 8. Ganon didn't get directly buffed much from Brawl (in fact he actually got a few nerfs which I do not understand at all)... but he did get a ton of indirect ones. Ganon isn't as bad this time around because the new mechanics are rather good for him (rage, no more change grabs, no more infinites, no more edgehogging, etc)
I think the rest of what most people consider as the bottom tier are fine at their places. Most of the characters at the bottom tier should stay bottom because other characters are simply just better. MK and Robin doesn't deserve to be called bottom tier. Ganon is the only overrated bottom tier IMO. I don't agree with Zelda being underrated. She's great but other characters are better. In my opinion, not counting Mii Swordfighter, either WFT or Lucy is the worst character in the game. Not much else to say about either because they're really just not that good... which is a shame because I love Lucy.
Again, this is my opinion on the characters that most would consider the "bottom". I just wanted to share my opinion.
