Editing tutorials

Basics
...
 * Choosing a level editor
 * Basics of the level format
 * Making a door
 * Making a switch
 * Making a teleporter
 * Aligning textures

Tricks
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 * Fake 3D platforms
 * Slopes

General guidelines

 * How to make a great level

WAD editing

 * Choosing a WAD editor
 * The WAD format
 * Adding custom textures
 * Adding custom sprites
 * Adding custom music
 * Adding custom sounds