Goku only uses the Super Kaio-Ken in DBZ once, but it's made several expanded universe appearances, such as a tool in Xeno Vegito's arsenal or the video games' Super Saiyan 4 Kaio-Ken combo.

Dragon Ball's Super Saiyan 4 transformation is a polarizing -- yet powerful -- form that's not as clear cut as fans may think.

That belongs to Xeno Goku and Xeno Vegeta as the pair are about to level up their Super Saiyan 4 forms. As you can see below, the new Dragon Ball key art shows off the Xeno fighters front and center.

Seeing Goku and Vegeta meet their Xeno counterparts is going to be fun – as will seeing SSJ4 Vegito on the battlefield. The Dragon Ball Heroes promo anime airs new episodes online.