In order to add more drama to a series which has been, up until that moment, lighthearted and comedic in nature, a villain (or antagonist of some sort) is introduced and is portrayed as a genuine threat, in contrast to the
bumbling and comedic villains the heroes have faced before. The
villian's arrival is sudden, and he is usually either a totally new character, or a character that has undergone a particularly dramatic Face–
Heel Turn.
Frizea from Dragon Ball Z is a Knight of Cerebus, Likewise, in the
Namek Arc, the fight with him is easily one of the most graphic in the franchise, consisting of torturous
beatdown after beatdown since it's an extremely one-sided fight till Goku turns
Super Saiyan.