Mega saiyan

Kill the Oozaru (Great Ape ) inside of you ( without cutting off your tail ) to become a "Mega Super Saiyan" (or Mega Saiyan), this results in your power being multiplied by 2000 times your normal form.

Achieved by:

The first one to use it was Trunks but Goku is the one who used it the best. This form have many different stages. It was said that this form rivals Infinty Super Saiyan, however it was later proven to be weaker than Super Saiyan 5.

Full Power Mega Saiyan
After 4 years this form was powered up to Full Power Mega Saiyan (more commonly known as SSj6). Full Power Mega Saiyan is like Mega Saiyan but with lighter hair.

You can do a Kamehameha x 1000 in this state.

All-Power-Mega Saiyan
This trasformation was powered up even more when Goegta used it. He powered it up to All-Power-Mega Saiyan. In this state your body is glowing beyond comparison. It was even used as a way to blind King Drain once.

All-Out-Mega Saiyan
Vegito took it to a power beyond compare. He transformed into All-Out-Mega Saiyan. In this state you out Mega Saiyan beyond it limit.

Meaning there rarely any chance it will damage your body.