Here is the full list of all 33 Ys: The Oath in Felghana achievements.
Beat the game in under 5 hours.
Beat the game on Hard.
"Killed" 50 immortal beasts without using the Silver Chimes.
Killed 500 Selnades across all playthroughs.
Sold Randolph's ring to Cynthia.
Killed 2,000 Mozgouz across all playthroughs.
Beat the game on Easy.
Beat the game on Very Easy.
Spent over 10 hours in a single playthrough.
"Measured" Elena.
Enabled "No-Fall" mode.
Began the game on Very Easy.
Beat the game on Normal.
Maxed out all equipment.
Acquired every jewel.
Saved all of Hugo's pikkards.
Encountered every enemy in the game, excluding bosses.
Spoke with every character in the game at least once.
Defeated 5 or more enemies (except Mozgouz) at the same time.
Completed Anya's treasure-hunt game.
Died over 10 times on a single boss.
Beat the game on Nightmare.
Beat the game on Inferno.
Conquered Boss Rush on Normal.
Conquered Boss Rush on Hard.
Conquered Boss Rush on Nightmare.
Escorted Elena to safety on every difficulty level.
Escorted Christof to safety on every difficulty level.
Achieved max level.
Defeated the final boss without taking any damage.
Bested the master of the mountains in one-on-one combat.
Defeated "The Deadliest Cuteness."
Completed all other achievements.