Here is the full list of all 4 Rainbow Laser Disco Dungeon Demo achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
You're actually playing it! Nice!
You completed the Tutorial! You probably know how to play now.
You did it... in Safety Dance mode. S s s s A a a a F f f f E e e e
Finish the demo? You did it! Like "did it" did it. Can you dig it?