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