One my main. Love megaman too. I guess none of his custom are good beside skull barrier?
A lot of his customs are pretty good to very good.
Bomb is like a weaker egg throw like you said, and there's some tech you can do with it.
Shadow Blade is good for close range pressure, and it can combo into usmash and grabs.
Beat allows you to go off farther below stage to edge guard and still make it back.
Tornado Hold is good, watch Ninjalink on YT on how to use this. It goes less high vertically but can be used offensively.
Danger Wrap is a side B that goes up at an angle with very good killing power. The default crash bomb is still great though just because of the mindgames you can do with it.
Ice Slasher has the niche use against superarmor moves, apparently freezing moves work really well against them.
DownB is preference. Skull Barrier for projectile users, Leaf Shield is weaker than Plant Barrier, can be thrown farther, and lasts longer, so it's personal preference for that. I prefer Leaf Shield for the easier edge guard shenanigans.
Doesn't Luma counter bananas?
As a Diddy player, not really. I can just throw the banana at Luma for some small free damage since it can't shield. It's really easy to short hop, uair Luma and separate the two, or go for a yolo sideB followup. Might get damaged but it can push Luma pretty far. Rosalina could downB to grab the banana, but I usually bait the Rosalina player into doing this since her downB has some cooldown. Allows me to go in and hit her in the face.
Battering Banana would send Luma upwards making it easy to separate the two as well. Diddy's fast and kills early so it gives Rosalina issues for sure.