Here is the full list of all 12 Nexuiz achievements worth 200 gamerscore.
Win a match in bot training.
Read the manual.
Win your first Quick Match!
Max out a Tier 3 Dynamic Mutator.
Use a Dynamic Mutator for the first time in a Quick Match.
25 Headshots in a Quick Match.
Use a CTF Dynamic Mutator to aid your team in a Quick Match!
Use 25 Dynamic Mutators in a Quick Match.
Kill 3 players in a row with melee attacks in a Quick Match.
Kill a member of IllFonic or someone who already has this achievement in a Quick Match.
Acquire 50 unique medals.
Played a match on every map in Quick Match.