Lionheart Dejimon Teimâzu : Season 1 Episode 34

As the gang meet up again they are quickly attacked by Beelzemon. However after Beelzemon kills Leomon, Takato, fueled by rage, forces Guilmon to Digivolve to his Mega Form – but it goes horribly wrong and Takato's D-3 Explodes, transforming Guilmon into the terrifying Megidramon.