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