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