Here is the full list of all 28 EMPTY SHELL: DEMO achievements.
Kill 350 Small Spiders
Death count: 10
Kill 400 Walking Soulless
Kill 10 Spitting Spiders
Collect all the documents in the Prologue
Kill 350 enemies with the Old Axe
Kill the Hand in less than 20 seconds on NIGHTMARE difficulty
As big as an elephant
Rounds fired: 200
Death count: 1
Kill her with her own weapon
Find 5 secret rooms
Rounds fired: 100
Find 5 documents
Deploy a Gadget
Use a Device
Kills count: 50
Upgrades Cost: >1000
Kills count: 15
Complete the Demo
Complete the Demo on Nightmare difficulty
Complete the Demo on Hard difficulty or higher
Complete the Demo on Medium difficulty or higher
Complete the Demo on Easy difficulty or higher
Survive the whole Prologue on NIGHTMARE difficulty with the same volunteer
Leaving Building C
Finish a level without taking any damaged on NIGHTMARE difficulty
Finish a level with only melee weapons