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