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