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