Full list of all 54 Enter the Gungeon achievements. It takes around 120-150 hours to unlock all of the achievements in the base game on Windows.
The base game contains 48 achievements, and there are 2 DLC packs containing 6 achievements.
Complete Frifle's Challenges
Collect five Master Rounds in one run
Ace Winchester's game 3 times
Kill 100 enemies by dropping chandeliers
Kill 100 enemies while riding in a mine cart
Open the shortcut to the Fifth Chamber
Unlock the Bullet
You've met with a terrible fate, haven't you
Clear the Sixth Chamber
Kill a Jammed Boss
Die in the Past
Open the shortcut to the Fourth Chamber
Steal 10 things
Clear the Fourth Chamber 20 Times
Clear the Fifth Chamber 10 Times
Complete all 4 main character Pasts
Kill the Convict's Past
Unlock the Robot
Kill the Pilot's Past
Kill the Hunter's Past
Open the shortcut to the Third Chamber
Clear the Third Chamber 30 Times
Populate the Breach
Win a wager against the Gunsling King 5 times
Access the Temple
Kill the Marine's Past
Complete the game with the Sorceress's Enchanted Gun
Construct the Bullet that can kill the Past
Clear the Second Chamber 40 Times
Clear the First Chamber 50 Times
Kill a frozen enemy by rolling into it
Accessed the Hidden Market
Carry a large amount of money at once
Map the first Five Chambers for the lost adventurer
Open the shortcut to the Second Chamber
Deliver the Golem's replacement arm
Kill 100 enemies by knocking them into pits
Get the jump on a Mimic
Spend big at the Acquisitions Department
Complete the game with Beast Mode on
Always be flipping. Guns are for flippers
Fall at the last second
Kill a boss after covering it with glitter
Why
Defeat the Boss of the Fifth Chamber
Avenge Manuel
Access the Oubliette
Complete the Tutorial
Complete Daisuke's trial
Kill the Bullet's Past
Kill the Robot's Past
Defeat an Advanced Boss
Take Revenge
Complete Tonic's Challenge