Flucifer is not seen in the game, and he is known as The Dark One. Flucifer was summoned by the Princess of Slimenia, who accidentally played a flute that summons him. The only way to defeat him was to use the Gott Schlieman tank, made by Alchemising the Schlieman and the Schwarzman. Flucifer possesses Don Clawleone once summoned, and uses a tank that looks like a Dragon.
The "Possessed Clawleone" is also seen in the Hero's Well, a fight in which you have to defeat him again, however, he has more HP and you have Swotsy, Hooly, and Bo on your team, and you have to protect them from his attacks.