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