Here is the full list of all 21 Before the Echo achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Defeat the Holiday Whompa.
Defeat an enemy with less than one second remaining on the clock.
Trigger Boost a Trigger Boost.
Defeat an enemy on the seventh floor using only Arclight.
Learn all spells.
See the hidden ending.
Queue up five spells in a row.
Defeat an enemy within eleven seconds.
Synthesize Iridium.
Synthesize every recipe in the game.
Beat the game on any difficulty.
Obtain every droppable item in the game at least once.
Discover the name of she who controls fate.
Defeat an enemy using only poison spells.
Get her back.
While learning a spell, achieve 100% accuracy for the entire song.
Successfully complete a synthesis at 25% odds of success or lower.
Recover over 150 mana in a single battle, and win.
Obtain all three droppable items from any single enemy.
Complete a battle without failing a spell.
Successfully defeat your first enemy.