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