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