Here is the full list of all 35 Adventure Time: The Secret of the Nameless Kingdom achievements worth 1,000 gamerscore.
Beat the game without upgrading Finn's Thumps, Sword, or Armor.
Get Extra Ending 2
Get Extra Ending 1
Get the true ending
Find every item in the entire game.
Max out your Thump Meter
Find every Baggy
Make a mess of the Pottery Shop until you get something nice
Locate the hidden Princess
Find Nightmare Princess
Defeat an enemy after hitting it with both Finn and Jake
Receive every type of Curse
Use Flambo to defeat a Lub Glub
Repair the wizard's door
Find every secret Gunter cave
Complete the Trading Game
Stun 5 enemies with a single Bananarang
Shove a Fairy Convict into a Baggy
Dance the night away in the Rave Cave
Receive sword training
Lie to Marceline
Win the race against Starchy
Squash a Pie Fairy
Find Slumber Princess
Buy any variety of Trail Mix
Attempt to speak to Stanley 5 times
Find a renewable light source
Appease Cinnamon Bun
Complete the circle of love
Find a Thump Shard
Chop down 999 bushes
Find Lullaby Princess
Buy an item from Choose Goose
Find a Gum Globe
Get briefed on the mission