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