Only Goku has mastered Kaioken, using up to x20 but never combining it with Super Saiyan. Combining Kaioken with SSJ is risky due to the emotional stress of SSJ affecting ki control. Kaioken is ...

Goku later uses Kaio-Ken x10 (or x20 in the English dub ... such as a tool in Xeno Vegito's arsenal or the video games' Super Saiyan 4 Kaio-Ken combo. The World’s Strongest is set early enough ...