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