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