This is one of the most entertaining features of the game. Using Ned, the in-game level editor, you have the ability to create your own maps. People who do this are known as mapmakers and/or neditors.
Before you even start Ned, you might want to come up with an idea for the map. Look at the top rated playable maps. Each revolves around a theme or concept. For example, What One Ways Were Made For by Sendy (NUMA) revolves around the idea that one way platforms can be used to create a maze. As the title states, it is what one-ways were made for. There are two kinds of ideas; tileset ideas and object ideas. Having both kinds of ideas will usually make a tileset more suited to the objects or vice-versa.
Draw the tileset
Visual appearance is one of the key factors that people judge their rating by.
If you have a tileset idea
Press J or H depending on your tileset idea. Now do it as you planned. You can put tileset-only decorations right here and now. If your level is a rocky level, add some cracks! If it's some foresty level, make it look foresty!
If you don't have a tileset idea
Now here, you're pretty much on your own. Some suggestions are
- Using the 'E' and 'D' tiles only, I draw some shapes, like a circle or something. Not a perfect circle, though.
- Smooth it out using other tiles, but I often make it craggly at the same time for visual appearance.
- Tileset-only decorations.
Make sure anything that would change the map is put down first (like mines blocking a path or some enemies, etc). Then place down your ninja in some place that 'works'. It's usually place it on a flat surface perpendicular to the ninja so that gravity will not move it. However, some maps put it somewhere else. If there is no perpendicular place to put a ninja, or if there is one but it just doesn't "work", then make one by modifying the tileset. Try to avoid spawning the ninja off the ground unless that was part of the idea.
Basic playability test
Playtesting isn't only just checking to see if a map is possible; it's also to tweak the map.
Go out into the debug menu, make sure Caps Lock is on and hit P. Just play around for a while, and note some bad places that lack flow. Flow means maintaining a good speed through the level, and not having to stop and figure out what to do next. Also note places that generally aren't fun. Places that are fun but frustrating are okay. That's what challenges are. You also need to note unintended things (a glitch, enemy path that doesn't work, etc).
When you're done fooling around in the level, go back and tweak the map so everything unintended is fixed or removed, the flow is fixed, and places that aren't fun are fixed or removed. Don't worry much about heavily editing, in fact, lots of fantastic levels start out looking completely different to how they end up looking. If you do feel insecure about editing a section, go ahead and save it into a text document and then try out the editing, if it doesn't suit just load the level from when you saved it.
The fun part.
Now you get to add objects. Some objects may have been placed already in Part Two, but now is the time to add the other ones that you didn’t get to add. Make sure you conform to Jeffkillian’s Map Making Guide while doing this.
Gold should be added sparsely. Just short, small bursts of gold will do. You may cluster gold, as long as it’s only around up to five clustered together (and usually one x-snap apart from each other will do). Overdoing gold ruins the map.
You can not only decorate with tilesets, but with objects as well! The most used (and best) objects to use for decoration are gold and mines. Gold can be, and usually is, used for not only increasing time, but decoration. Mines can make maps harder and decorate at the same time. It can be used solely to make maps harder, or solely to decorate as well. Try to avoid using mines to solely make maps harder.
Don’t cluster enemies. That should be explained in Jeffkillian’s guide. In fact, you should cluster nothing else.
As for the rest of the objects, I can't help you there.
Yet another playability test
The last step.
As you always do, make sure that the level is beatable. And if you intend for people to go for all gold, make sure that getting all gold is possible. Make sure that the objects you added makes it even better and maybe slightly harder. Don’t make something insanely hard. No one generally likes insanely hard maps, with some exceptions. You have to make maps that the most amounts of people will enjoy. If it's fun for you then other people will probably enjoy it as well. Tweak anything that's wrong as you won't modify the map any further.
Come up with a name for the map, save it on your hard drive, show it to your friends, submit it on NUMA, whatever, you're done! And don't forget to break the rules, these are all guidelines! P.S Always think outside the box.