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