Here is the full list of all 24 Nadir: A Grimdark Deckbuilder achievements.
Defeat King in Yellow
Defeat Chernobog
Defeat Minos
Defeat Asmodeus
Earn any Desires for the first time
Defeat Lilith
Earn any Idols for the first time
Defeat Koschei the Immortal
Defeat Moloch
Defeat Abaddon
Defeat the Gunnery Demon
Earn any Skulls for the first time
Defeat Fury
Earn any Filth for the first time
Earn any Relics for the first time
Defeat Feaster from Afar
Play the Saint's Blood card
Possess a Damned as a reward
Defeat Belzebub
Unlock Hernan Cortes as a playable character
Unlock Vlad Tepes as a playable character
Defeat Beelzebub
Obtain any Rare card
Purchase any card in the shop