Here is the full list of all 20 Mystical Map achievements.
Use your first map item.
Hold all 6 map items at once.
Hold more relics than you can handle.
Beat your first combat room.
Fight a mimic for the first time.
Beat your first bullet hell room.
Reach the item in a platforming room.
Defeat the Minotaur at the end of the forest.
Defeat the Oculothorax at the end of the mine.
Defeat the Samurai at the end of the cave.
Maximize an upgrade's level.
Kill 100 enemies in one playthrough.
Maximize every upgrade's level.
Hold 10,000 ink at once.
Defeat the Minotaur while taking no damage.
Defeat the Oculothorax while taking no damage.
Defeat the Samurai while taking no damage.
Change unique weapons 10 times in one playthrough.
In one playthrough, defeat the final boss without picking up a weapon once.
In one playthrough, defeat the final boss without picking up a relic item once.