A Day in the Life of a Bun Trophy in Adventure Time: The Secret of the Nameless Kingdom

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.

Cinnamon Bun is blocking the way to the lower right area of the map. When Finn talks to him, Cinnamon Bun wants to see something funny. To appease him and gain entry to the area he is blocking you must first have at least one empty baggy (see The Pods for baggie locations) and already have Grabby Hand (which you will get in Song Temple) then travel to Medium Butt Rock, located 1 screen down, 3 screens left, then one more screen down from Pillowmint Butler's castle. You will find a dancing green puff of smoke right below the rock. Slap it up to put it in a Baggy and take the Baggy of Poot to Cinnamon Bun to give him a good laugh that will make him teeter off the bridge and open up a section of the map you will need to proceed.