Here is the full list of all 24 Undead Horde achievements.
Kill six humans with a single scythe sweep.
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.
Sell 20 skulls.
Claim all areas in Burning Rock.
Claim all areas in the Catacombs.
Claim all areas in Alwyn.
Use ring of plague to infect the living via chickens.
Raise a horde of 50 undead.
Raise 1000 corpses.
Command a single unit to kill 20 enemies.
Chickenify a dire wolf.
Summon a hero from a hero statue.
Reach level 5.
Raise 15 corpses at once.
Slaughter 100 chickens.