Aren't You Thankful? Achievement
Aren't You Thankful?50
Complete the game on Hardcore Mode.
Hardcore Mode is unlocked after completing the game on any difficulty. This is default at Hard difficulty mode. You cannot die. Checkpoints are active, but once death occurs, you will have to start over. Your best bet is to make a backup save, and every so often save to it just in case. This makes it not so "hardcore" but if you want the achievement without hassle, this might be your ticket.