Here is the full list of all 13 Code Arcturus achievements.
Complete any level in NERFED mode
Complete all levels in NERFED mode
Beat any level's par time in SPEEDRUN mode
Beat all level's par times in SPEEDRUN mode
Miss the par time by less than a second for any level in SPEEDRUN mode
Beat the level Escaping the Swarm
You didn't grow. You didn't improve. You took a shortcut and gained nothing. You experienced a hollow victory. Nothing was risked and nothing was gained. It's sad that you don't know the difference.
Fire 10000 bullets from your blaster
Beat the final boss
Beat the level Deeper Descent
Find and collect all gems in the game
Beat the level Prickly Predicament in Nerfed mode
Unlocked the Triple Jump upgrade