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