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 Beast.
Why?
Finish the demo with the Damsel.
Finish the demo with the Spectre
Finish the demo with the Adversary.
Finish the demo with the Stranger.
Finish the demo with the Nightmare.
Finish the demo with the Razor.
I can't believe you gave her a knife.
Finish the demo with the Witch
Finish the demo with the Prisoner.
Finish the demo with the Tower.
I don't know.
Did your best to resist, but in the end, it didn't even matter.
Finish a staring contest with the Princess.
Die at least 6 times across all playthroughs.
Start Chapter 2 and get the heck out of dodge.
Die.
You did it! You saved everyone!