Here is the full list of all 16 Demon's GunPlay achievements.
Use the "Joker"
Defeat 50 Succubus or Monsters
Defeat 100 Succubus or Monsters
Defeat 150 Succubus or Monsters
Defeat 200 Succubus or Monsters
Defeat 300 Succubus or Monsters
Beat the cave demon
Beat the prison demon
Beat the forest demon
Beat the tower demon
Get Crimson Ruby
Get Azure Orb
Get Emerald Gem
Defeat the Boss Succubus
Defeat the Queen Succubus
Complete the game in normal mode