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