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