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