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