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