I've heard pacman is really bad, but I've never had a problem with one. That said, there's like <5 actually good Pacmen in the world, so all of us have very little experience. Figured I'd throw him on the list out of respect and lack of personal knowledge.
Greninja is super even, imo. he has a way of getting inside and punishing that very few characters do. Actually, I'm now curious how you could consider Fox a bad matchup, but Greninja a very good one, as their strengths are similar (good mobility, general low-risk moves, fast falling, good combos/punish game, and decent killers). I'd actually argue that Greninja has safer approach options, better air mobility, and similar damage output/killpower, so I'm really curious on this one...
Diddy and Sonic are both no worse than even, imo. I actually think Mega vs Diddy is among Diddy's current worst matchups.
Lucario is interesting. If he had no aura mechanic, the matchup would be firmly in our favor imo. I do think we win the spacing game to a rather large degree on him. the fact that he starts killing so early is problematic, but I don't think the matchup is extremely negative, because our tools can consistently keep him out, so it just becomes a matter of whether or not we can kill/avoid his killers.
Gotta say, I think you and I are just going to disagree on matchups. Could be a difference in region or playstyle, but you considering Pika, ZSS, Mario, Fox, and Yoshi bad matchups just blows my mind, honestly, and goes against the majority Megaman opinion for at least several of these (ZSS in particular)..