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