Saiyan Saga

• The Saiyan saga featured the introduction of Saiyans, an alien warrior race that actively conquers planets. Saiyans have significantly higher power levels than any human on Earth at the time; this was a severe contrast to the low power levels during the original Dragon Ball series. Even Goku, the protagonist Saiyan raised from Earth, was outclassed by saiyans such as his brother Raditz and his eventual rival, Vegeta. The numerical range of power levels during this saga is between zero and 10,000, from the basic martial artist to beings capable of firing large destructive energy beams.
  
  

Frieza Saga

• The Frieza saga largely took place on Namek, an extraterrestrial planet. Transformations were first introduced during this saga. Each transformation indicated a significant increase in power -- typically in multiples from the original form. Frieza, the main antagonist during this saga, had four transformations. This saga also introduced the Super Saiyan transformation, one of the most iconic transformations in the entire series. As a result of the events of the saga, Goku involuntarily transformed into a Super Saiyan, multiplying his power level by 50 times. Numerical power levels ranged between 100,000 to 1,500,000. A being with a power level beyond 500,000 can destroy entire planets.
  
  

Android Saga

• The Android saga centered on the destructive androids, Earth-made artificial beings designed to kill Goku. Most of the androids had undetectable power levels; this made it difficult for the protagonists to gauge their true strength. Absorption was also first introduced in this saga. Cell, the main antagonist, absorbed both humans and androids to increase his power level. Most of the characters had power levels of over 1,000,000 during this saga, the highest being in the 30,000,000 level.
  
  

Majin Buu Saga

• The Majin Buu saga was based around an artificial extraterrestrial being called Majin Buu. This was the saga where most of the protagonists were significantly weaker than the antagonist: Majin Buu had all of the heroes' techniques, can regenerate from the smallest atom and can survive interplanetary explosions. Furthermore, Majin Buu can also absorb other people to increase his power. Both the heroes and the villains have such extremely high power levels that they outmatched the most high-ranking authority in the universe, the Supreme Kai. The majority of the power levels during this saga fall between 30,000,000 and 100,000,000 -- all capable of destroying galaxies with ease.