Here is the full list of all 25 Hybrid achievements worth 400 gamerscore.
Reach Rank 50 after going Elite for the 5th time
Win a Season
Complete a Season
Unlock Rank 1 Elite
Reach Tier 5 in all Specializations
Achieve 2 kills with a single shotgun blast
Complete 50 Missions
Achieve 50 total kills with your Preyon
Achieve 50 total kills with your Warbringer
Reach Rank 25
Achieve 50 total kills with your Stalker
Achieve 3 kills at once inside the King Zone using Core Breach
Achieve 3 consecutive kills without landing at a Cover
Reach Tier 5 in a single Specialization
Win a game of Overlord as the Overlord at the end of the Match
Unlock a weapon from each category
Squad Hack a Preyon to kill its original owner
Achieve a kill while inside a Smoke-Chaff cloud
Win a round of Tactics after being the only player left on your team
Get executed by an enemy Preyon while using Taunt
Equip a different helmet for your character
Achieve 3 kills at once using a single Grenade
Achieve 15 kills in a single Match
Complete a Mission
Complete the Tutorial