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