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