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