Here is the full list of all 17 Legend of Long Night achievements.
Acquire 25 Cards
Acquire Summoners
Acquire Sky Disrupters
Acquire Raging Skeletons
Acquire Dominators
Acquire War Drumcarts
Acquire Shadow Assassins
Upgrade the Nazgul King to Lv13.
Upgrade the Light Priest to Lv13.
Upgrade the Gnome Doctor to Lv13.
Upgrade your character to Lv15.
Complete all Common stages in Chaos.
Complete all Common stages in Templar.
Complete all Common stages in Gnome.
Reach Tier 8 Arena.
Reach Tier 10 Arena.
Defeat your opponents 3 times in a row.