Here is the full list of all 12 Nexuiz achievements.
Use a dynamic mutator for the first time
Use a CTF Dynamic Mutator to aid your team!
Killed 3 in a row using melee attacks
Kill a member of IllFonic or someone who has already won this trophy
Taken bot training
You read the manual
Won your first game online
Max out medium cost mutator
25 headshots
Use 25 Dynamic Mutators in a match.
Awarded 50 unique medals
Played a match on every map