Diabolus

Diabolus (邪竜, Jaryū) is the mastermind behind the events of Bladestorm: Nightmare. A vile dragon that feeds on death and despair, it was summoned by a descendant of a forgotten tribe who sought revenge against England and France for their continued wars. The creature devoured the man's soul and used Joan of Arc as its vessel to sow fear and mistrust among the humans.

The monsters it conjured devastated the royal armies to such a degree that not even their combined might was enough to turn the situation around. But as the humans steadily subjugate the creatures with the Gladius Dux, Diabolus slowly loses control over its host. The protagonist's victory over the possessed Joan expels the dragon from her body, though the destruction it previously caused allows it to gain a corporeal form.

After failing to kill the maiden, it revives the defeated monsters to distract the English-French alliance while building up its own forces at Cocherel. However, the collective hopes of the survivors weakens it enough for Joan and the protagonist to mortally wound it. Denied of their feelings of despair and sorrow, the dragon is destroyed for good.

Fighting Style
As the largest unit in the game, Diabolus must have its defenses worn down repeatedly before the player can damage its multiple weak spots. The dragon has several dangerous attacks at its disposal, so using stat-boosting pennons and switching between different troops is a must in order to survive.