Here is the full list of all 46 Adventure Time: Explore the Dungeon Because I DON'T KNOW! achievements.
Complete a Quest for the Princess.
Upgrade a character's Thumps.
Return from the Dungeon alive.
Use a Special Attack.
Perform a Perfect Block.
Buy something from the shop.
Outsmart the Demon Cat.
Outrun the stampeding prisoners.
Put Ice King in his place.
Assist Gunter with a feisty feline.
Rescue the Hyoomans.
Weather Goliad and Stormo's psychic assault.
Free the Earl of Lemongrab.
Free Flame Princess.
Overcome the Guardians' punishment.
Uncover Bubblegum's dark secret.
Upgrade a character's Rowdiness.
Upgrade a character's Focus.
Upgrade a character's Imagination.
Fully upgrade Finn.
Fully upgrade Jake.
Fully upgrade Marceline.
Fully upgrade Cinnamon Bun.
Fully upgrade LSP.
Fully upgrade Ice King.
Fully upgrade Lemongrab.
Fully upgrade Flame Princess.
Complete all of Princess Bubblegum's Quests.
Complete all of Tree Trunks' Quests.
Complete all of Susan Strong's Quests.
Complete all of Mr. Pig's Quests.
Complete all of Starchy's Quests.
Enter the Nightosphere.
Receive a Curse.
Survive 15 Floors in one Nightosphere run.
Survive 25 Floors in one Nightosphere run.
Survive 50 Floors in one Nightosphere run.
Grab 50 Treasures on a single Treasure Floor.
Survive a Monster Floor
Collect every Token.
Collect every Sub-Weapon.
Upgrade a Sub-Weapon into a stronger one.
Eat every Food item at least once.
Locate every Familiar.
Find all of BMO's Game Cartridges.
Pick up every Item pickup at least once.