Here is the full list of all 20 NEON Ultra achievements.
Die for the first time
Achieve a 10x Combo
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Achieve a 300x Combo
Achieve a 600x Combo
Survive for 120 seconds without shooting once
Kill 100 enemies without taking damage
Amass a score of 500,000 in one game
Amass a score of 777,777 in one game
Amass a score of 1,000,000 in one game
Amass a score of 5,000,000 in one game
Amass a score of 10,000,000 in one game
Played 50 full games of NEON Ultra
Played 100 full games of NEON Ultra
Keep a shield active for 60 seconds
Kill 100 enemies in one game
Kill 500 enemies in one game
Kill 800 enemies in one game
Reach maximum weapon power
Kill 15 enemies without moving