Ōzaru 大 猿 - Great Monkey - is a skill that allows the Saiyan with their tail to become a giant ape if they expose themselves to the light of the full Moon multiplying their power their power.
The ability to transform into Ozaru only affects the race of the Saiyan or Saiyans and their hybrids with humans. But if you are a Dragon Ball fan this is better than good.
What you may not know is that transformation is possible (in theory) thanks to Bruits waves product of the reflection of a sun on a moon. When these waves come into contact with your eyes you are excited by the glands charged with initiating the transformation, which are found exclusively in their tails. This explains why they can only be transformed if they have the tail in perfect condition.
Some Space Warriors like Vegeta or Tullece know a technique called Power Ball. They have the ability to create a cluster of energy capable of emitting Bruits waves. This was used in combat to conquer planets quickly, turning all the surrounding Saiyans into beasts.