Here is the full list of all 27 Impostor Inside Us achievements.
Die First Time
Die 5 Times
Die 10 Times
Die 20 Times
Die 50 Times
First Time Is Impostor
Kill First Time
Kill 5 Times
Kill 10 Times
Kill 20 Times
Kill 50 Times
Kill 100 Times
Lose First Times
Lose 5 Times
Lose 10 Times
Lose 20 Times
Lose 50 Times
Complete Quest First Time
Complete Quest 100 Times
Complete Quest 10 Times
Complete Quest 20 Times
Complete Quest 50 Times
Win First Time
Win 5 Times
Win 10 Times
Win 20 Times
Win 50 Times