Here is the full list of all 26 Demented Pixie achievements.
Vanquish 200 enemies in a single run
Reach the City of the Wailing Lights
By now you should have learnt to evade traps
Consume the finest hearts for your own benefit
Defeat Faer at the City of the Wailing Lights
Defeat Elva, the Queen of Reflections
Defeat Saghe and live in the wilds
Destroy the Moon of Reflections
Live in an empty world
Reach the root of the problem
Collect 500 crystines in a single run
Beat Ig, the apprentice
Beat Mushka, the Wind Virtuoso
Sacrifice your belongings
Die in the wilds
Survive the skull path
Survive the Tower of Greed
Do the 27 thing and win
Win a run in Hard Mode
Identify 5 scrolls in a single run
Die 15 times
Get poisoned... a lot
Defeat Angus
Die 5 times
Defeat Toril the charred
Die 25 times