From the Mystara Mailing List posted 02 June 1998.
Power Points: 300
Armour Class: 0 (Full Plate)
Hit Dice: 22*********
Hit Points: 110
Move: 120' (40')
Attacks: One Weapon (Longsword, Lance, Mace or other Knightly weapon)
Damage: by weapon (all Shadowknights have at least one magical weapon. If the Weapon Mastery rules are used, Shadowknights are Grand Masters of one Weapon and Master of two weapons.)
No. Appearing: 1 (1d8+1)
Save As: IM1
Treasure Type: Varies. All have at least one magical Weapon. Intelligence: 1d8+27
Alignment: Neutral (AD&D: Lawful Evil)
XP Value: 25,250 (2PP)
Monster type: Humanoid
Shadowknights are humanoid creatures dressed in Full Plate mail armour completely hiding their bodies. It is said that if someone should ever see a Shadowknight's face, he will be struck with madness. Their armour and weapons are completely black as if made my solid darkness. The Shadowknights rarely speak. When they do, they speak with a rasping voice that sends shivers down the spine of the bravest warrior. Although, servants of darkness, they are still Knights and have a sense of honour. They will never refuse a challenge, and will respect a worthy opponent.
Shadowknights are the servants of Thanatos. When, encountered outside Thanatos' homeplane they are always on a mission from their master. These missions can be finding artifacts, protecting important mortals or places, destroying special people or places or other. They often use Nightmares as mounts though some have found other even more dreadful creatures that they use.
Shadowknights often work alone. However on very special missions groups of knights found led by an officer armed with a Longsword of slicing+5. The leader always has maximum hit points.
Special abilities: Shadowknights are exalted creatures who can be killed. Like Immortals they can spend TP to gain the abilities of 36th level spellcasters. They do not need to eat sleep or breathe. They are Immune to energy Drain, disease, ageing and Immortal-level ESP spells. The Knights only have one form and can not have a mortal identity. It takes a weapon +3 or greater to harm them. They have Anti-Magic, but are affected by moral magic.
Characteristics: Ability scores are determined using 1d8+27
Where found: anywhere.