After reaching the Elven Kingdom, talk to Jimmy to start this quest. Set him as your buddy then go to the barn to trigger a scene. Rancher Bill will give you the key so head to the barn and defeat the nazi zombie cows. Take note that these bastards will blow themselves up if you used a group attack that severely injures them but not enough to finish them off.
Loot the bodies and go left. There's a chest here that can only be accessed once you have Gnome Dust that will make your shrink. Climb the ladder then shoot the lamp to break it. Fart on the open flame to remove the haystack. Loot the flute from the item bag and leave the barn.
Jimmy will become your friend afterward.
I seem to have finished the game but still have yet to complete this mission. It's not allowing me to have/use any buddies. Is there a way to still complete this mission? Thanks- Candi