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