Here is the full list of all 35 GALAK-Z achievements.
Rescue Admiral Akamoto
Collect every crate in every Mission in a single Season
Shield parry 25 bug attacks
Complete Mech Tutorial
In Season 2 or higher, complete a Mission without collecting any Salvage
Kill 3 enemies with a single explosion
Deflect 20 shots with the Mech sword within 10 seconds
Slay White Tusk
Complete Intro Tutorial
Complete a Mission without being noticed by the enemies at the warp point
Steal the Void Raiders' Star Map
Defeat the Raider King
Complete a mission without getting hit
Defeat 500 Space Bugs
Defeat 500 Imperials
Defeat 500 Void Raiders
Complete the game on Rogue difficulty
Destroy every segment on White Tusk's body
Kill White Tusk in under 30 seconds
In Season 2, only defeat enemies while in Mech form
Kill a Sentinel within one second of alerting it
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
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 3 attacks in a row from Uzzerach Nam without taking any damage
Feed a grappled enemy to a cave spider
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