[Appearance could be similar to the Adeptus Custodes from Warhammer 40,000)
The Praetorian Guard
The Emperors Bodyguards and the elite of the Empire's forces.
Behold: The Mighty Praetorian Guard. The finest warriors the Empire has ever known. Ever since childhood, they have been trained in the arts of combat and warfare. They carry glaives into battle, and are gifted with the strongest armor the Empire can provide: Adamantium Armor. With these, the Praetorians can slaughter dozens before being taken down. Though generally at the Emperors side, a few of the Empires generals have the honor of having Praetorians under their service.
Fearless: Praetorians are taught that dying in the service of the Emperor is the greatest glory that they can achieve in their lives. As such, even when outnumbered, the Praetorian will not be deterred. He will fight his enemies to the death, no matter how many he will face.
Adamantium Armor: The highly durable adamantium armor that they wear increases their defense. However, once by 50% of their health, they will loose the defense bonus that the adamantium provides.
War Cry: The Praetorian shouts a fearsome war cry, briefly paralyzing his opponent/s in fright.
Impale: The Praetorian impales his target with his glaive that deals a considerable amount of damage and will stun his opponent for a few moments.
Whirlwind Attack: The Praetorian swings his glaive around for a few seconds, damaging multiple enemies within his attack range.
Preferably, the Praetorians would be enemies encountered during the final levels of the campaign. Also, only a few of them should be encountered (preferably 2 or 4), since obviously a dozen/dozens of them can make situations Really difficult. If an Empire Campaign would ever be implemented, or if the Empire is Playable during Skirmish mode, then the room requirements to summon Praetorians would be akin to the Dark Angels from DK2 (Only 2 can be summoned at a time).
Feel free to share your thoughts with this idea. Criticism is highly recommended. And please Do Not be gentle.