Here is the full list of all 20 The MISSING: JJ Macfield and the Island of Memories achievements.
Acquire every donut.
Read all of F.K.'s hidden texts after finishing the game.
Read all of the texts from the past.
Find every Sleepy.
Crane operation is dangerous work.
Read a hidden text from F.K. after finishing the game.
Select Continue after the ending and start a new run.
Complete the game.
Reach the top of the clock tower.
Escape danger.
Don't get too addicted to your phone.
Fall off a bridge.
Get run over by a train.
Escape from something scary.
Jump over that black thing!
Find the first Sleepy.
Chat with F.K. for the first time.
Let the strange deer empower you.
First, you need to find Emily.
Awaken at the campground.