Eh, I have heard Mega goes even with Weegee. Here are my thoughts.
I do believe Crash Bomber and Metal Blades get whupped by Fireballs. The only thing Fireballs lose is Mega Buster (And Charge Shot. But it's transcendent). Though, Luigi Cyclone plows through them all. It's a theory, but considering Cyclone plows through Samus' missiles.... it should be eating lemons there.
I have fought a pro Mega player, pre-patch (And yes, I got whupped hard), and..... his lemons are certainly a problem. Unpredictable Cyclone usages can help. Remember, MegaMan has end lag on the third shot, so he can't fire those lemons like madman. It's REALLY REALLY small though.
Aerial.... his air speed trumps ours. Flame Sword has fair amount of end lag I believe, B-air is annoying (It kills and edgeguard, just like Luigi's), U-air is, well, undoubtely unique, but all you need is either get out of the way or airdgodge, really. In my experience, his first try to juggle with this usually succeed, sending me high up. Then his second attempt.... I just airdodged it up high and he can't really do anything about it except to punish our landing. That ledge! Remember! (Or FF N-air if you're real). Mega Buster is as annoying as ever, but I don't believe he will be using it often, they go in a straight path. Hard Knuckle meteors, hard. Don't eat it by recovering high.
We must keep one thing in mind, we must not let him space his attacks, or else we're done. His aerials, especially.
His F-smash is one of the weakest smash attack in power, but it is an edgeguarding legend. DO NAWT RECOVER IN A STRAIGHT LINE! Like I said, recovering high is our best option here, but if he is expecting this, mix things up.
U-smash has much more range than it looks, trust me. I learned this the hard way. Otherwise, it's your usual 'landing punisher' attack.
D-smash is his second most powerful move, FLAME BLAST! (Dat is the right name right?) Though, unless it has been patched, the animation decieves. It may look like Mega is protecting himself with the pillar or flames during the attack, and you can't seem to punish it.... until you realize there are no hitboxes othe rthan the earlier frames..... yeah, the animation decieves. However, be cautious, it is his second most powerful attack, and apparently it got some range, and he can also punish your landing with this. If you successfully dodged this attack though, burst through the harmless flames and let the comboes begin!
Mega Upper, alright, it is FJP's small bro. Yes, SHORYUKEN! Yep, it may not look like it, but it's MegaMan's most powerful move. Somewhat like Ganon, having an U-tilt that is stronger than his smash attacks.... Anyway, it comes out quick, but somewhat punishable on whiff, and in order to sweetspot it, he has to breath on your face.... just like Fire Jump Punch. However, it is weaker, but less punishable (Thus, why the 'small bro' lol). Remember, this move is his strongest attack, outclassing even his U-smash and D-smash in terms of power.
His F-tilt is his 'moving Mega Buster' alright.
D-tilt is somewhat annoying too.... it covers lots of distance, and after Metal Blade, Mega can follow up with this, and it puts you to the air.
In short.... Mega wins if he manage to outcamp Luigi and outspace him..... but that's about it. Luigi crushes him in melee combat (Mind his Mega Upper and tilts! And Flame Blast and Spark Shot!) and once we're in, we must not let him get away. Hillariously enough, his dashing speed is slower than Luigi.
Crash Bombers are somwhat hillarious. If we get caught, bump with Mega to transfer it to him, effectively making him has to shield or dodge away. This can mess him up, but remember! The blast will still hurt you! Don't get bombed!
Leaf Shield can somewhat edgeguard you (Cancels out jumps), but Mega can't do anything besides grabs I believe. But no, if he throws this, get away, just get away or shield. Fireballs won't cancel this out, and while it deals little damage, still an annoyance.
In a nutshell, this is like Zelda MU. He manages to outspace and outcamp or just keeps you away, he wins. Luigi manages to get in (Which.... I do believe is manageable), Luigi wins. One of the best Mega players in GFAQs (Yes, he was the one I fought), said Mega vs Luigi is even, but doesn't say why (Maybe because he is making a MU chart for MM, but no one asked for Luigi except me, but he didn't replied).
Take this with a grain of salt. I rarely ecounter good Mega online now. I'll need to do some more research. But for now, I think it's even. That F2 N-air is interesting though, can it breaks through double F-airs?