Here is the full list of all 37 Secret of Mana achievements. It takes around 25-30 hours to unlock all of the achievements on Windows.
Reach the ending
Defeat Mana Beast
All weapons at level 9
Complete the guide
All magic at level 8
Defeat all monsters
Defeat Dark Lich
Obtain all torso gear
Obtain all head gear
Defeat Dread Slime
Defeat King Vampire
Obtain all arm gear
Defeat Blue Dragon
Visit all locations on Flammie
Defeat Mech Rider 3
Defeat Kettle Kin
Defeat Aegagropilon
Defeat Dark Stalker
Defeat Shadows #1, 2 & 3
Defeat Gorgon Bull
Defeat Lime Slime
Defeat Mech Rider 2
Defeat Vampire
Defeat Minotaur
Defeat Mech Rider
Defeat Frost Gigas
Defeat Boreal Face
Defeat Great Viper
Defeat Spring Beak
Defeat Jabberwocky
Defeat Kilroy
Defeat Wall Face
Defeat Fire Gigas
Defeat Biting Lizard
Defeat Spikey Tiger
Defeat Tropicallo
Defeat Mantis Ant