During first opening cinematic with the son and father sitting around the fire, repeatedly select the fire so that the room remains lit for the entire scene.
Easy "Role reversal" achievement
An enemy is "defeated" by killing it in the same manner that a player dies; for example, falling a large distance, colliding with spikes, walking in exploding black goo, etc. You must kill different enemies. An enemy is considered the same if it appears from the same point at the start of the level.
Various Tips and Tricks
Keep in mind that the boy and his father will beckon the other if he needs some help.
If you stick near fires you'll stay warm.
Make sure you leave the other character in a safe place when you wander off.