Kaio-Ken

Kaio-ken ( 'Kaiōken', lit. "Realm King Fist") is a technique invented by King Kai; however, Goku is the only person ever to use it successfully. It is a technique that multiplies the user's ki for a "heartbeat" - thus increasing their power and speed and enabling them to inflict serious damage to opponents who are considerably stronger than them. However, the downside of the Kaio-ken is that it takes a heavy toll on the user's body.

Information
When you transform you gain a red aura.

There are multiple kaioken forms: Kaio-Ken - Kaio-Ken x3 and Kaio-Ken x10 - Kaio-Ken x20

Kaio-Ken and Kaio-Ken x3 can be gained by talking to king kai in the other world and they require level 15.

Kaio-Ken x10 and Kaio-Ken x20 can be gained by talking to king kai in the other world just like the first 2 ones, they require level 50.

All Kaio-Ken forms damage your health, the higher the Kaio-Ken level the more health you lose, for an example, you lose more health in Kaio-Ken x10 than in Kaio-Ken x3, you lose more health in Kaio-Ken x3 then in Kaio-Ken, you get the point.