I did this from scratch. It's unrelated to the previous versions in this thread, but it looks like geod wants us not to make multiple threads for the same game.
Mega Man 2 is the first MM game I ever beat. I was dropped off at a friend's house early in the morning, waiting for the bus to school. It was still dark out. We busted out MM2 and played it through to the end. The very emotional and melancholy tone of the ending will stick with me forever. We were on top of the world that day.
MM2 is a huge improvement over MM in that the platforming is sturdier (falling off of moving platforms didn't make you plummet, and you had better control in mid-air to land on ledges), and the bosses are for the most part much more fair. The music is some of the best in the series, too. MM2 was far from perfect and it suffered from some odd design choices, but it's little wonder that this game launched the series into popularity where the first entry had failed to.
I worked on this over the course of multiple days, and actually had to start from scratch a total of three times due to the 3dn save bug. These start-overs, combined with my need to backup and check after every level, made this project take as long as it did. Hopefully the bug will be less frequent in future releases of 3DNes.
The less deleterious bug where "Cube" and "FullCube" patterning leaves huge gaps in walls/floors/ceilings is still present here, but I decided that when it looks good, it more than makes up for the times it does not due to the bug.
One of the first things you might notice is that unlike my MM1 work, the energy bars are prisms instead of cylinders. This was necessary due to the way MM2 displays energy bars in the main menu. The flattened look has kind of grown on me. We'll see what the other games allow for.
You might also notice that the clouds in Air Man's stage are in the foreground, but do not obscure Mega Man. I really wanted them to be able to, but the interior of the clouds share their data with the background of the menu. To make the clouds obstructive would mean to make the main menu illegible.
Furthermore, that cloud data is actually shared by the sky portion of Wood Man's stage, and the entirety of Crash Man's stage. As a result, I sadly had to make those sections flat. The same thing had to happen with the first portion of Wily stage 1. The only way I could see these being satisfactorily resolved is if a future version of 3DNes allows you to change fore/background properties of an individual color in a palette. I don't see this ever happening, so those stages will remain as flat as they are in the meantime.
The giant gears in Metal Man's stage that make up the floor had to be made flat, since a lot of their sprite is the "transparent" color that greatly factors in to how cylinder shapes are calculated. Late in that stage, there are horizontal gears that I was able to make cylindrical, at least.