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