Great ape

A Great Ape(Oozaru) is a form saiyans take when they still posses their tails and look at a full moon. This makes saiyans somewhat similiar to the fictional legend of werewolves. It was stated by Vegeta that the reason they trasnform is because of them absorbing over 17 million zeno threw their eyes then turning on certain glands in thier tails "then the transformation begins" stated by Vegeta. The user completely loses all self control and memories unless they been trained to but only elite saiyans are trained how.

Usage and Power
In this form saiyans power increases tenfold. As stated by Vegeta in the Saiyan Saga. Therer power and endurance seems to increases greaty they seem to lack speed but they can keep their speed if they control themselfs in that form.