The moment you’ve all been waiting for has finally arrived; the level editor for Super Meat Boy is now live on Steam! It’s currently technically in a beta phase but you can use it to create any level you want excluding the minus world type levels and bosses. To access it after you’ve updated, check under “Tools” in your Steam Library (a shortcut will be added shortly to make accessing the level editor easier). You can create levels for any character, whether or not you have that character unlocked.
For more details on how to get your levels updated or what you need to do to make a level, check out the original blog post by Team Meat.