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