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