Sonic has matches that allow him to compete with some of the higher/top tier characters. Big example imo is Diddy Kong, whom you can use his own banana game against, and reduce the use of it thanks to the mobility of the Spin Dash/Spin Charge going right over any bananas, not to mention the ease in rolling over a banana and picking it up with a quick and difficult to punish dash attack. Take away Diddy's Banana game and you just have a character with a good FAir, a quick DAir spike and an FSmash you can SDI out of. A good Sonic can render Diddy's banana game severely limited. On top of that, Sonic isn't as pressured against Falco's laser game for how quickly he closes that gap, and anyone who makes the mistake of buffering the CG wrong gets a spring to the face and unlike other quick characters like Marth who leave themselves vulnerable if they use a Dolphin Slash to disrupt someone, Sonic has one of the best options. The only real flaw is that he has to come down sometime, but he can air dodge/do anything at that point.
Snake is ridiculously heavy, and like DK can usually be read into a good 50%+ combo from the get go with a good UThrow > UThrow > UAir > BAir, and if you read them even better or they don't DI correctly, another BAir, then wait for them to come back down with a DSmash. that's way more then 50% right there. Sonic has great options when used correctly. And unlike most other lower tier'd characters, against the likes of Meta Knight, it's not Sonic's worst nightmare either.
Of course, this is all my opinion, and no one has to take my word for anything I say in regards to the tier list discussion. But seeing as how others gave their input when I asked, I thought I might as well give my own.
Sonic is definitely a Middle Tier character, and whether he goes up or down, so long as he does not leave C-Tier, then I say he's justified.
Pokémon Trainer is definitely a Mid-Tier character though. It's difficult to consistently use and master all 3 characters. That's like having 3 equally usable mains without one being better then the other in your hands. Tough as heck man. Ivysaur simply gets shafted with it's terrible recovery. If he had a good recovery and his Vine Whip worked differently, then Ivysaur would actually be a good character.