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