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