Here is the full list of all 33 Ys: The Oath in Felghana achievements.
Beat the game on Very Easy.
Beat the game in under 5 hours.
Acquired every jewel.
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.
Saved all of Hugo's pikkards.
Sold Randolph's ring to Cynthia.
"Measured" Elena.
Completed Anya's treasure-hunt game.
Enabled "No-Fall" mode.
Began the game on Very Easy.
Beat the game on Easy.
Beat the game on Normal.
Beat the game on Hard.
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.
Died over 10 times on a single boss.
Achieved max level.
Defeated the final boss without taking any damage.
Spent over 10 hours in a single playthrough.
Maxed out all equipment.
"Killed" 50 immortal beasts without using the Silver Chimes.
Killed 2,000 Mozgouz across all playthroughs.
Killed 500 Selnades across all playthroughs.
Bested the master of the mountains in one-on-one combat.
Defeated "The Deadliest Cuteness."
Completed all other achievements.