: This is a missable achievement, since you can mix destroying and keeping the things, annulling the Catharsis
After progressing through the story and obtaining the ability to manipulate fire, you will come back to the tree house. There, Finn will wait for you and kind of "explode", setting four piles of stuff on fire.
Simply draw fire (
) from one pile and add it (
) to the brasier outside. You have to do this for every one of the four piles, saving all the stuff and granting you the achievement.Look out for the other achievement!After obtaining this achievement, the game won't autosave until after you speak to Finn again, so just quit the game and reload it by selecting "Continue" in the main menu. You'll start again at the bottom of the ladder leading to the tree house, allowing you to go for the Catharsis achievement without starting a whole new playthrough!