THE SUPER SECRET FEATURES FROM RTWD
Warning: Contains major spoilers. Don't read this if you want to find out by yourself!
Load the editor. Press CTRL-F6. You will now have two new icons. One is a spooky green statue and the other is a "w"-icon.
The green statue works like the regular statue and can be placed on a wall.
To make the "w"-icon work, you must change the background to "Rainbow". Place the "w"-icon anywhere in the level (like you do with weather and color icons), and you have a rainbow level.