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