Just go in and kill him. This sounds simplistic but seriously it's the answer. The Hero sucks at landing, has an exploitable recovery, has generally poor frame data, and his specials all reward him for charging or fooling with menus and further he recovers MP for time passing at that. Every incentive in the world is there for you to rush the guy down and just kill him before he gets to do anything useful. If you play defensively, respect everything that might happen even though most of the time Hero hits down-B he won't have that one special ready to shut you down, and try to just react to his stuff and counter what you see coming, you're probably going to lose every time so just... don't do that. Obviously this thought process works best if you play a fast character like Fox or Pikachu that benefited a lot from playing this way otherwise, and you're probably going to struggle if you main someone like Mega Man who doesn't really take to these types of tactics. If you do play a projectile character or someone who necessarily has to go at a pace slower than breakneck, at a minimum, be sure you're always pressuring him. The main thing the Hero needs to get going is time, and therefore, your primary objective should be depriving him of that whenever possible. Make the game about him fearing what you're doing and worrying whether he'll ever get a chance to do his stuff; this is often good advice in general, but Hero really emphasizes the importance of controlling the match for yourself more than other characters.
If I'm being honest, I think Hero seems dead middle at best and probably lower mid. He's really fun to play and I really enjoy him, but he's just so slow and really flat out lacking in truly solid answers to aggression and fast play. I think as a counterpick character he'll prove to have immense value since he is really good at countering specific problematic characters and playstyles, but I know I'd be terrified to actually main this guy. He just has too many downsides, and in the context of tournament play where the most important thing is winning a lot of games in a row, having more RNG than everyone else definitely highlights the downsides of RNG more than the upsides. Of course, a character this complex can never be written off quickly, but I'm just not optimistic things will work out for him.