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.
Claim all areas in Burning Rock.
Kill six humans with a single scythe sweep.
Use ring of plague to infect the living via chickens.
Chickenify a dire wolf.
Sell 20 skulls.
Raise 1000 corpses.
Raise a horde of 50 undead.
Claim all areas in the Catacombs.
Raise 15 corpses at once.
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.