From Diablo Wiki
Headcleaver, "Royal Executioner", is a superunique Skeleton that features as part of The Legacy of Cain quest. He appears in Leoric's Passage accompanied by his Royal Henchmen. They all have melee attacks but Headcleaver also has a nasty kick.
Headcleaver is involved in the following Achievement.
| Cut Off the Head
|10||Kill Headcleaver before killing any of the Royal Henchmen who arrive with him in Leoric's Passage.|
You can kill the initial bunch of Skeletons you see when you get down there but not the ones that Headcleaver actually spawns with. It's best to stand back and let him spawn with his minions so the pack splits up a little as they pursue you, it's easier to pick them off without inadvertently killing him too soon.
|Monsters of Diablo III Beasts Beasts: Superunique Demons Demons: Superunique Humans Humans: Superunique Undead Undead: Superunique Objects Bosses Boss Mods Monster Info Fanmade|
Bat - Beast - Blood Hawk - Demonic Hellflyer - Electric Eel - Khazra - Lacuni - Lamprey - Quill Fiend - Rockworm - Sand Monster - Sand Shark - Sand Wasp - Scavenger - Spider - Spiderling - Swarm - Withermoth - Wood Wraith -
|Primary Quest Uniques||
Act One Bosses:
Skeleton King -
The Warden -
Strong CC (Limit 1): Knockback -- Nightmarish -- Vortex -- Jailer
|Act One Uniques||Araneae - Web Spit||Leoric - Summon Skeleton, Teleport Strike, Triple Cleave||The Butcher - Smash, Grappling Hook, Spear, Frenzy Charge|
|Act Two Uniques||Maghda - Forcefield, Summoning Ritual, Punish, Moth Dust, Teleport.||Zoltan Kulle - Fiery Boulder, Time Bubble, Ceiling Collapse, Energy Twister,Vanish, Creepy Laugh||Belial - Phase One: Triple Fireball, Summon Vipers. Phase Two: Poison Meteors, Ground Pound, Lightning Strike, Lightning Breath.|
|Act Three Uniques||Ghom - Acid Slime, Sneeze, Gas Cloud, Chomp.||Siegebreaker - Triple Hit, Charge, Leg Stomp, Grab and Throw.||Cydaea - Pain Bolts, Web Trap, Spider Pits.||Azmodan - Bellyflop, Laser Attack, Falling Corpses, Demon Gate, Pool of Destruction, Globe of Annihilation.|
|Act Four Uniques||Rakanoth - Cleave, Teleport Strike, Blade Strike, Volley, Summon Minion.||Izual - Frost Nova, Frozen, Summon Minions.|| Diablo - Phase One: Claw Rip, Charge, Hell Spikes, Shadow Vanish Grab, Curse of Destruction, Ring of Fire, Ground Stomp, Curse of Anguish, Curse of Hatred. |
Phase Two: Shadow Clone. Phase Three: Overdrive, Lightning Breath.