Quest: Chesty's Chest
Location: Sunset House
How to Complete: After Mourningwood Fort Battle has finished you'll follow the trail to your next destination. You will come across a large set of open gates on the left just beyond a graveyard. Enter through the gates to transition to Sunset House.
Once in this region, make sure its night (if not exit then re-enter the region). Head to the gazebo to the left and interact with a statue 4 times, then move across and do the same thing with the others. You're trying to move them to the stances they were in during the day. When done right the house will change from a ghostly residence to the real thing.
Enter the house, read the letter and then sleep in the bed. You'll be transported to a life sized chest board. Once there speak to Chesty to make the game begin. If you don't know how to play don't worry as Chesty will cheat!
Just play until he lobs bombs at your pieces and changes the rules. Then defeat each wave of enemies to survive the game and unlock the achievement.