Here is the full list of all 30 Tiny Tina's Assault on Dragon Keep: A Wonderlands One-shot Adventure achievements.
Killed a Chubby
Completed level 1 of all challenges with a single character
Reached level 35
Completed all side missions
Had Purple-rated gear or better equipped in every slot
Demonstrated your skill, or lack thereof, at rolling the magical treasure orb of many sides
Vanquished the Ancient Dragons of Destruction
Remained in Zero's Deception mode for ten seconds straight
Won the most challenging round in Murderlin's Temple
Reached level 25
Gunzerked continuously for 90 seconds
Showed thine worst enemy, the abomination known as "The Darkness", who is the nerdiest of them all
Wielded the Mysterious Amulet
Fed thy noble queen 3 times during one visit to her quarters
Completed thy quest by rescuing yonder queen
Completed the mission "Shoot This Guy in the Face"
Killed 100 enemies while using Buzzaxe Rampage
Killed 100 enemies with Deathtrap
Killed 100 enemies with the Sabre turret
Phaselocked 100 enemies
Unlocked 10 customization items
Used the Lootapult to cause a Lootsplosion
Redeemed 25 tokens
Purchased 5 items from the black market
Reached level 10
Unsheathed 5 swords from Immortal Skeletaurs without leaving the area
Introduced thyself to the White Knight
Reached level 5
Slew Mister Boney Pants Guy
Revived someone from "Fight for Your Life!" that is on your friends list