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