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