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