Here is the full list of all 16 ARKOS achievements.
Find a secret scroll on E5M01
Find a Dopefish on E2MXX
Find a secret portal on E2M03
Сross the level boundary on E2M01
Find a secret scroll on E1M03
FInd 20 secrets
Pass the level without damage
Kill 1000 enemies
Collect 50 big health potions
Find insane difficulty portal in a Hub
Kill 500 enemies
Collect 50 big mana potions
Break 100 objects
Master the teleport power
Escape from the river of lava on E1M03
Kill 100 enemies