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