Here is the full list of all 50 20XX achievements.
Complete the game with 1 or fewer maximum HP.
Complete the game with Rock and Purist active.
Complete the game having taken damage ten or fewer times.
Complete the game with Wrath, Famine, Marathon, and Toxin active.
Complete the game with High Tide, Marathon, Wrath, Undying, and Destiny active.
With the High Tide Skull on, complete the game without picking up any maximum health upgrades.
Die 50 times.
Complete the game with Final Destination active.
Without Bankrupt active, complete the game without picking up any nuts or nut-granting Augs.
Complete the game with at least 3 Prototypes and no System Restore.
Complete a Marathon run within 35 minutes.
Complete the game with Marathon, Famine, and Bankrupt active.
Complete the game with Wrath, Undying, Furor, and Swarm active.
With the Undying Skull on, complete the game without picking up any damage upgrades.
Clear Level 40 in Endless Mode.
Clear Level 25 in Endless Mode.
Unlock everything in the Soul Shop.
Win 250 Slot Machine prizes.
Complete 10 Daily Challenges.
On Level 8, defeat both Twin Astrals with falling platforms.
On Level 8, defeat all four Rollsters within a single three-second window.
Have 50 Maximum HP at once (Endless Mode not eligible).
On Level 8, defeat Shatterbeak without letting him use any interruptible abilities.
On Level 8, defeat Kur after reflecting all of his Quint Laser attacks.
On Level 8, survive for 60 seconds without taking damage during The Perforator fight.
Complete a Daily Challenge.
Complete the game within 28 minutes.
Complete a Rush Job.
Clear Level 16 in Endless Mode.
Equip four non-matching Cores at the same time.
Complete a Core Set.
Have 250 nuts at once (Endless Mode not eligible).
Start a third run in a single game session.
On Level 8, defeat Vile Visage by breaking his horn while he's at or very near full health, then only using basic (including charged) attacks.
Destroy a vending machine -- a victimless crime.
Complete the game with the default primary weapon and no Powers.
Don't touch any surfaces for 10 seconds (Endless Mode not eligible).
End a run with at least 50 Soul Chips.
Complete the game after entering and achieving glory in all Glory Zones.
Complete the game with 8 Powers.
Complete the game.
Complete the game with 1 HP remaining (and no armor).
Forsake your only true friend.
Complete level 8.
On Level 8, defeat Death Lotus with 10 Lotus Spawns alive.
Complete level 4.
Deliver a boss' killing blow with its weakness.
On Level 8, defeat 50 Flapps and Eternal Star within two seconds using Force Nova.
Clear level 1 with Bankrupt, Famine, Furor, High Tide, Marathon, Purist, Rock, Swarm, Toxin, Undying, and Wrath active.
Clear level 3 with Bankrupt, Famine, Furor, High Tide, Marathon, Purist, Rock, Swarm, Toxin, Undying, and Wrath active.