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