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