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