Here is the full list of all 19 Slay the Princess Demo achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Finish the demo with the Adversary.
Finish the demo with the Spectre
I don't know.
Die.
You did it! You saved everyone!
Did your best to resist, but in the end, it didn't even matter.
Finish a staring contest with the Princess.
Finish the demo with the Prisoner.
Start Chapter 2 and get the heck out of dodge.
Finish the demo with the Razor.
I can't believe you gave her a knife.
Finish the demo with the Tower.
Finish the demo with the Witch
Die at least 6 times across all playthroughs.
Why?
Finish the demo with the Stranger.
Finish the demo with the Beast.
Finish the demo with the Damsel.
Finish the demo with the Nightmare.