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