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