Here is the full list of all 16 Amaranthine achievements.
Complete game on legend mode
Reach 20 level on legend mode
Sell 100 weapons
Destroy the overwatcher
Destroy 5000 enemies
Kill 10 enemies in 1 secon
Ram 50 enemies
Complete game on normal
Destroy the battlecruiser
Destroy 12 cargo ships in a single run
Find legendary weapon
Complete subwarp level
Destroy 1000 enemies
Destroy the bomb
Destroy 250 enemies
Complete level without taking any damage