Here is the full list of all 24 Undead Horde achievements.
Start a New Era.
Find and complete all quests.
Claim all areas in the Citadel.
Claim all areas.
Explore all areas.
Claim all areas in the Wastelands.
Find all secrets
Unlock all the basic statues.
Acquire the legendary Necronomicon.
Gain a million gold.
Claim all areas in Burning Rock.
Sell 20 skulls.
Raise 1000 corpses.
Use ring of plague to infect the living via chickens.
Chickenify a dire wolf.
Claim all areas in the Catacombs.
Summon a hero from a hero statue.
Claim all areas in Alwyn.
Reach level 5.
Slaughter 100 chickens.
Raise a horde of 50 undead.
Command a single unit to kill 20 enemies.
Kill six humans with a single scythe sweep.
Raise 15 corpses at once.