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