Here is the full list of all 35 GALAK-Z achievements.
Complete the game on Rogue difficulty
In Season 2, only defeat enemies while in Mech form
Kill 3 enemies with a single explosion
Deflect 20 shots with the Mech sword within 10 seconds
Feed a grappled enemy to a cave spider
Complete Mech Tutorial
Slay White Tusk
Rescue Admiral Akamoto
Steal the Void Raiders' Star Map
Defeat the Raider King
Complete a mission without getting hit
Kill White Tusk in under 30 seconds
In Season 2 or higher, complete a Mission without collecting any Salvage
Kill a Sentinel within one second of alerting it
Complete Intro Tutorial
Complete a Mission without being noticed by the enemies at the warp point
Defeat 500 Space Bugs
Defeat 500 Imperials
Defeat 500 Void Raiders
Destroy every segment on White Tusk's body
Kill a Sentinel by throwing it into Akamoto's Escape Pod
Destroy the Overpowered Sentinel using only grappled missiles
Rescue Admiral Akamoto within 3'00"
Collect 5,000 Salvage in a single Season
Collect every crate in every Mission in a single Season
Kill an enemy with each of the Elemental upgrades in a single Season
Shatter 25 frozen enemies
Kill 3 enemies with a single pierce shot
Kill at least 3 enemies with a single spike spore without taking any damage
Shield parry 25 bug attacks
Shield parry 3 attacks in a row from Uzzerach Nam without taking any damage
Fully upgrade both health and shields in a single Season
Kill every enemy in a single Mission in Season 4
Complete Season 4 without using any missiles
Complete Season 4 without acquiring any upgrades