With the 1.1.0 update we've unlocked the level editor for everyone to use!
This is the full featured version of the level editor that we used to build every level in the game. It comes with features to edit terrain, monsters, and scripts to build anything you can imagine.
We will be posting a detailed guide on how to use the editor soon. Until then you can unlock the editor by going into the Options Menu and setting the "Level Editor" option to On.