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