Here is the full list of all 21 CASTILLO: Shattered Mirrors achievements.
Enter the woods
Enter harrismouth
Enter the farm
Kill Dracula
Meet William
Begin your journey
Enter the hidden level in the basement
Enter the naughty list
Enter the forest
Enter the carnival
Enter the sewer
Enter the spaceship
Enter the darkness
Enter the shores
Enter the cabin
Enter the swamp
Enter the resort
Enter hell
Enter the cursed village
Slay the Phantaconda
Slay the large rat