Here is the full list of all 46 Demon Peak achievements.
Defeat the Master of the Arcane Tower
Kill an enemy with a reflected axe
Kill an enemy with a reflected arrow
Collect first Health Pickup
Collect all Health Pickups
Collect first Essence Pickup
Collect all Essence Pickups
Break dozens of barrels
Acquire a total of 999 Gold
Defeat the Monster of the Infested Lake
Defeat the Scourge of the Monastery
Master all abilities
Acquire the Air Dash ability
Acquire the Light Dash ability
Acquire the Heavy Dash ability
Acquire the Ground Shattering ability
Acquire the Demon Wings
Acquire the Water Mastery
Acquire the Demonic Hammer
Acquire the Hammer Combo ability
Acquire the Hammer Air ability
Acquire the Demonic Spear
Acquire the Spear Charge ability
Acquire the Dive Kick ability
Acquire the Super Kick ability
Acquire the Uppercut ability
Acquire Uppersmash ability
Acquire Demon Eyes
Use a Sub Weapon to kill an enemy
Kill an enemy with a reflected spin attack
Cause a Mage to kill another enemy with its attack
Map every room in the game
Acquire at least one of each Sub Item and Weapon
Use the Life Elixir to save yourself from a certain death
Slay hundreds of enemies
Finish the game without Saving
Finish the game without the first Powerup
Finish the game without dying
Finish the game in 45 minutes or less
Finish the game