Here is the full list of all 46 Obey Me achievements.
Defeat Billy
Defeat Ors
Defeat Ximala & Dranea
Defeat Marchosias
Defeat The Purifier
Defeat The Angelical Echo
Defeat Anna
Defeat Ammon
Defeat Zadkiel
Complete The Slums
Complete Clota's Open Mall
Complete Beneath the City
Complete Legion Bank
Unlock All Dog Forms
Unlock All Weapons
Finish the Game with 100% Completion
Stay Fused for 666 Seconds
Defeat 1,000 Enemy Units
Locate all cute graffiti in Chapter 7
Destroy all the Ancient Radios
Trigger 1,000 Charged Enemies
Get an SS Rank on any Encounter
Find one of Crowley's Notes
Find all of Crowley's Notes
Complete a Purified Astral Crystal
Collect all Purified Astral Shards
Collect 300,000 Souls
Defeat Chapter 2's boss without taking any damage
Defeat Chapter 3's boss without allowing it to heal
Defeat Chapter 6's first boss in less than 100 seconds
Defeat Chapter 6's second boss without allowing him to transform
Defeat Chapter 8's boss without allowing it to use its tornado attack more than two times
Defeat Chapter 9's boss without losing more than 20% of Vanessa's health
Defeat Chapter 11's boss after making her clones attack her at least once
Defeat Chapter 12's first boss without being hit by orb attacks more than three times
Defeat Chapter 12's second boss after triggering him at full charge three or more times
Fully upgrade a weapon
Fully upgrade all weapons
Fully upgrade a dog form
Fully upgrade all dog forms
Achieve a SS rating on any chapter
Defeat the bosses of Chapters 2 and 3 on Hard Mode
Defeat the bosses of Chapter 6 on Hard Mode
Defeat the bosses of Chapters 8 and 9 on Hard Mode
Defeat the bosses of Chapters 11 and 12 on Hard Mode
Clear all chapters with S rank or higher