Here is the full list of all 11 cyber_serpent achievements.
Beat training mode
Die 100 times
Beat challenge mode
Beat challenge mode without collecting pickups
Beat challenge mode without dashing
Get a score of 25k or more in infinite mode
Get a score of 50k or more in infinite mode
Get a score of 100k or more in infinite mode
Get a score of 25k in infinite mode without collecting pickups
Get a score of 50k in infinite mode without dashing
Unlock all achievements