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