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