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