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