Here is the full list of all 35 Adventure Time: The Secret Of The Nameless Kingdom achievements.
Beat the game with 3 thumps, without upgraded sword, shield, or armor
Choose Lullaby Princess to rule
Choose Slumber Princess to rule
Choose Nightmare Princess to rule
Find everything in the game
Find all thump shards / spare thumps
Complete the Trading Game quest
Find all five baggies
Break the pot breaking record
Complete sword training
Complete the Dungeon Drama quest
Complete the Fear Temple
Kill an enemy after both Finn and Jake have attacked it
Receive every curse
Stun 5 enemies with a single Bananarang
Talk to Stanley five times
Find every Gunter cave
Complete the Door Repair quest
Party in the Rave Cave for 11 minutes and 12 seconds
Lie to Marceline
Use Grabby Hand on a Pie Fairy
Store a Convict Fairy in a baggy
Beat Starchy's Graveyard Fun Run
Complete the Dream Temple
Kill a Lub Glub using Flambo
Complete the Terrible People quest
Complete the Cinnamon Fun! quest
Complete the Love Note quest
Buy any trail mix
Chop down 999 bushes
Find a thump shard
Complete the Song Temple
Find a gum globe
Buy something from Choose Goose
Complete the tutorial