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