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