Here is the full list of all 9 Magicians' Legacy: Prologue achievements.
Defeat the skeletons at the portal.
Convince Ivy to let Oriana go.
Improve any spirit.
Win 5 battles.
Apply unit abilities 5 times.
Spend 100 Mana.
Bring water from the well to Ulmus.
Equip 5 artifacts on a hero.
Defeat Cyclops Ajaxis.