Here is the full list of all 10 Project Blue Book: Hidden Mysteries achievements.
Use 20 hints
Earn max stars on all hidden object scenes in a case
Play 20 minigames
Play each type of minigame at least once
Play 6 'Hidden Object' scenes
Complete one 'Found Object' Scene
Investigate 6 leads
Unlock a new episode
Get a streak of 8 objects
Complete a scene in under 25 seconds