Here is the full list of all 44 Nuclear Throne achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Reach 4-? as Crystal.
Reach 7-3 on a Daily.
Loop as every character.
Defeat Hyper Crystal as Horror.
Eat a Hyper Weapon as Robot.
Unlock a Golden Weapon for every character.
Unlock Hard Mode.
Defeat the Technomancer.
We hereby sincerely apologize.
Defeat Horror.
Reach 2-? as Eyes.
Unlock a Crown as any character.
Defeat Hyper Crystal.
Reach 5-?.
Defeat Mom.
Reach Level Ultra as any character.
Die.
Reach 2-1.
Reach 3-1.
Reach 6-1.
Reach 5-1.
Loop past the Nuclear Throne.
Reach the Nuclear Throne.
Defeat Lil Hunter.
Defeat the Nuclear Throne.
Defeat Throne II.
Loop the game.
Defeat Big Dog.
Unlock a Golden Weapon as any character.
Reach 3-?.
Defeat Big Bandit.
Reach the Nuclear Throne with Melting without choosing Rhino Skin or Strong Spirit.
Reach the Nuclear Throne in under 10 minutes as Plant.
Defeat the Technomancer as Steroids.
Reach 2-1 on Hard Mode as Chicken.
Defeat Mom as Rebel.
Defeat Captain as Rogue.
Unlock a Golden Disc Gun or Golden Nuke Launcher.
Reach Level Ultra as Skeleton.
Play as Frog.
Sit on the Nuclear Throne as headless Chicken.
Unlock all Crowns as one character.
Defeat Captain.
Get 100% of the unlocks.