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