Megidramon

Megidramon is a Mega Level Evil Dragon Digimon who it also one of the Four Great Dragon Digimon. He is a rare species whose reason for existing is unknown, but have something to do with the Digital Hazard, a power that is sealed away by some other "force." However, when that power is awakened, he creates a system meltdown which could destroy the Digital World. It is theoried that he can Slide evolve to ChaosGallantmon. His name comes from Megiddo, the place where, in Christian tradition, the final battle between good and evil, Armageddon, will take place.

Digimon Tamers
Angered by Leomon's death at the hands of Beelzemon, Takato forced WarGrowlmon to Digivolve to Megidramon. Horrified by this transformation, Takato could only watch as Megidramon and Beelzemon went head to head, the end result being Megidramon's defeat. Takato cried, knelt down by the unconscious Megidramon and wished that they could fight Beelzemon together as it should be, which resulted in him Biomerging with Guilmon to become Gallantmon.