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