Kaioken

From the anime Dragonball Z, Kaioken is the fighting technique taught to Goku (the only one to master this technique) by King Kai. Though King Kai created this technique, he admits that not even he is able to fully master it. The technique is very similar to going super saiyan, although the power increase is not as high, it is very effective before Goku first transforms. Goku discontinues using the Kaioken attack after his fight with Pikkon, opting instead to attain high super saiyan levels. The technique only last a few seconds according to Goku so you "have to get the job done quickly". It momentarily greatly increases your speed, strength and abilities, allowing you to achieve a power level unobtainable without the use of this technique. Through experience and training, the user can achieve multiple 'levels' of Kaioken, increasing the users abilities even further. However, according to King Kai, if you go up too far, your body will not able to handle it, and all the mass in your body will be replaced by energy, thereby making it explode. Goku is able to withstand a 4x Kaioken while fighting Vegeta, (putting his fighting power well over 23,000) in order to counter his Galick Gun attack. However, after this feat his body is thrashed and has no other way of attacking other than using the spirit bomb, another technique exclusive to Goku and King Kai. Cell states that he could use this technique if he wanted to, however.