Single-player only
Difficulty does NOT affect achievements
Steam achievements do work offline
No missable achievements (plus 9 unknown)
Sign in with Steam or Xbox to track your progress, and:
Level up your Hero to level 1
Buy some equipment for your Hero
Level up your Hero to level 4
Complete 1 quest
Open all elemental elements
Create all 3 towns
Create all magical creatures.
Invent all spells
Create all elements in Main Game
Level up your Hero to level 10
Complete 3 quests
Buy 10 belongings for your Hero.
Level up your Hero to level 16
Level up your Hero to level 21