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