Here is the full list of all 16 ITTA achievements.
Keep Itta's Dying Mother Company For 1 Minute After Talking
Defeat All Bosses Without Dying
Collect All Spirit Cats
Collect All Spirit Weapons
Kill Mono Only Using The Revolver
Complete ITTA
Receive Inner Beast's Spirit Blast
Open The Void Gate
Complete The Shepherd's Story
Collect All Heart Upgrades
100% Map Completion
Enter The Yorke Ruins
Receive Inner Beast's Homing Spirits
Complete The Architect's Story
Receive Inner Beast's Fire
Enter The Glass Garden