Press "G" to hide/unhide the editor grid Press "B" to cycle through backdrops Press "Q and "E" to cycle through level parts "notice the red cross that is the eraser" Aside from the mouse you can use arrow keys and space to place blocks, note that each placed block count towards the clone limit.
Here's another indev build for my upcoming port of the game Professor Fizzwizzle. I am open for feedback, of course anything in the indev builds are subject to change Shoutouts to Big Fish Games, formerly Grubby Games!!