Double click flag? Once the message is done, press space. You can make it say whatever you want! Underscores, which look like _, are used for spaces. Don't put a space after a comma. (Yikes this thing has bugs. Need to stomp them flat before I put this in the game!)
This engine is probably the first time I've ever utilized custom blocks like this. The engine is made for my in-development game, Doodleworld, ( https://scratch.mit.edu/projects/847324427/ ) and I'm pretty proud of it! (There are some bugs!)
