(For those wondering how to make a Sprite be a Temporary Wall, simply Add a Message, but I'm sure most people know this by now.
For a Permanent Wall, I'd guess from playing all WW Games so far but 1 [Nancy Goo just won't Load!], unless people have made new ones on their itch.io Profile that IDK about [which is very possible!]: they seem to be Invisible Tiles that are on the Same Level as your Avatar [only way I know of, since that'll stop you from falling off Ledges and into Holes].
Also, Reload WW Editor WebPage to Make a New Game, as the 'New Game' Button Makes a BUG'd Room [1 small block to stand on]! I find it much like Minecraft and Luanti that WW defaults to a Room where you're FORCED to build onto the existing Block Tiles rather than be able to Draw where you want, same as you MUST Copy/Dupe Room 0 and use Invisible Sprites for Exits in order to Make "New" Rooms.)
The MAIN THING this Game Engine needs really badly is the ability to ERASE SPRITES From Rooms!
It's so annoying placing a Sprite by Mistake, only to realize that the only way to "Delete" it from a Room is to Copy a Sprite and make it Invisible, but even then (eg. if you need to see those Sprites, you can Fill with a Solid Color), you can quickly make Multiples of said Sprite in a Room that way, so you're not actually getting rid of Sprites.
Please add a way to Erase Sprites from Rooms so that this cute editor will have the Much-Needed function it's been lacking! Thank you!
One more thing if you can: a Rotate Map (Room) feature would be amazing (having to Zoom on a Certain Part of a Room just to "Move" the Room to where you want it is frustrating!).
Oh, and maybe a way to Place Tiles fast WITHOUT that Glitch (you know the one, where if you keep holding down, the Tiles Automatically Pile-Up on each other!).
Keep up the good work! :D