The Enchiridion! Trophy

Story Related, cannot be missed.

Many of the fetch quests built into the game are related to progression through the story as they will give Finn and Jake either, entry into a new area or a new ability that will allow further progress later on so this trophy cannot be missed even if it does not seem to be connected to the main story per se.

When visiting the Graveyard, Finn can talk to a Nightosphere Demon who requires some Bug Milk. Getting him the Bug Milk will be necessary in order to open the way to the final temple, Pillowmint Butler's Castle, where you start the game. You do not need any Baggies to carry the items for this fetch quest as they are stored in a separate part of Finn's Inventory:

• Once you obtain Grabby Hand from Song Temple, go to the abandoned house next to Choose Goose's Store and grab the book on the bookshelf, The Heat Index
• Head 2 screens down and chop the single bush next the castle wall to reveal a hidden staircase. Give Shelby the movie and he will give you Mind Games
• In the top left corner of the map is the Ice King. Bring him Mind Games, he will return the favor by giving Finn some Fanfiction.
• In the swamp area, 1 screen down from the Totally Freaky Dungeon you will find a cave. Inside is a mean Coal Man. Give him the Fanfiction and you will receive the Honey Energy Drink
• Head to the Rave Cave (see The Party's Over if you don't know where it is). Give Party Pat the Honey Energy Drink and he will give Finn the Bug Milk
• Return to the Nightosphere Demon in the Graveyard. Speak to him to hand over the Bug Milk and he will give you the Enchiridion which will translate the ancient text written on the giant stone slabs throughout the map, namely the two stones you will need to read to open the entrance to the final temple towards the end of the game