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