Mausoleum Knight
Mausoleum Knights are headless knights who command the Mausoleum Soldiers and Foot Soldiers. They carry greatswords, partisans, greatshields and greatbows.
The first one most players meet stands on the Bellum Highway outside the Black Knife Catacombs. Others are in Liurnia of the Lakes north-east of the Academy of Raya Lucaria, in the Consecrated Snowfield and around the Nameless Eternal City in the Deeproot Depths, where some ride headless steeds. Knights near a Wandering Mausoleum stop respawning once you have used that mausoleum.
Drops
Partisan
Eclipse Crest Greatshield
Greatbow
Mausoleum Knight Set
Great Arrow
Weaknesses
Resistances & immunities
How to beat it
Fight a Mausoleum Knight as you would any armoured knight: wait out its combos, punish the recovery and keep an eye on stamina. Greatshield users need heavy hits or a way around their guard, and greatbow users should be rushed or fought from cover.
The mounted knights in the Deeproot Depths are a different fight. Watch their charges and punish them as they turn.
Lore
The Mausoleum Knights of Castle Sol cut off their own heads to serve their masters in death, a curse that tied their souls to the land. Their leader, Lhutel the Headless, gave her life to keep serving a soulless demigod until its revival, and she was honoured with an Erdtree Burial for it.