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