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