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