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