The Destruction of Planet Vegeta
Vegeta was already aware that the destruction of Planet Vegeta was the work of Frieza in the anime. However, in the manga, just like Raditz, Vegeta believed that it happened due to a meteor strike. Changing the story of the anime to suit the screenplay may have been a bad decision. It would have been a true warrior’s despair when he would learn about the evil of Frieza for the first time.
Breathing In Space
On Planet Namek, when Frieza attacked, one of the threats to the Z fighters was that if the planet exploded, Goku will have no atmosphere to breathe. The fighters had to use special pods instead of flying themselves to space. But in Dragon Ball Z: Battle of Gods, Goku can breathe and fight in the space without any repercussions.
Missing Tails
Gohan was born with a tail. He could also turn into the great ape. But soon after the first few arcs of DBZ, the idea of tails was scrapped. Trunks and Goten never had a tail. Gohan mysteriously never grew back his tail. Any other Saiyans introduced in the series had no tails either.
Cell’s Regeneration Powers
Cell could regenerate his limbs as he was given the DNA from Piccolo. But, he was also seen regenerating his whole body in one instance. That ability made no sense and Piccolo cannot do such a thing.
Krillin’s Height
In Dragon Ball Z anime, Krillin’s Height has remained inconsistent. He looked like a little kid even though he was supposed to be an adult. The animators fixed this later in the anime but it left some weird impressions behind.
Hair Growth
Vegeta once stated that full-blooded Saiyans have no hair growth after they are born. They have the same hair throughout their life. But, Portion of Goku’s hair was chopped off once that grew back later.
Over 9000!
The famous phrase “Over 9000” from Dragon Ball Z was a mistake by the Voice Actor. The original translation was “Over 8000”. The dub made it to the general public after all as no one noticed.
Afterlife concept
The afterlife concept of the Dragon Ball is especially nonsensical. It was originally stated that only the true of Heart can retain their bodies after Death. But, later we found out, that all the villains manage to retain their bodies. Also, why are the general humans don’t retain the bodies more often?
Old Kai’s Mystery
The origin of Old Kai’s rough looks was that he accidentally fused with an old witch through Potara fusion. We later find out that this fusion can only stay true for 30 minutes.
Power levels
Initially, the power levels were measured according to the Scouter used by the Saiyans. But after the transformations to SSG forms, the difference in power levels between Saiyans and other humans doesn’t make sense anymore. The gap is too great.
Gohan vs Goku
Dragon Ball Z tried to set up Gohan the main character in both the Frieza and Cell Arc. “The son of Goku who would transcend him in power.” But as we all saw, Gohan was reduced to a family guy who is not even close to the power levels of his father.
No Consequences
The Dragon Ball series has such a story that there are no consequences in the end for the main characters. They always seem to transcend to the powers of the villain and fix any damage using the Dragon Balls.