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