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