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