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