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