Super Saiyan 4 Kaio-ken

Kaio-ken has a long history as a stackable technique in Dragon Ball. Goku first used it in his base form against Vegeta during the Saiyan Saga, and later combined it with Super Saiyan Blue during the Tournament of Power in Dragon Ball Super. The principle is consistent: Kaio-ken multiplies whatever power level the user currently has, making it more effective the higher the base form.

Applying Kaio-ken to Super Saiyan 4, which is itself an extraordinarily powerful transformation, produces results that are proportionally extreme. In Super Dragon Ball Heroes, this combination is used in situations where standard SS4 is insufficient against particularly powerful adversaries, providing a short but dramatic power boost.

Risk and Reward

The danger of combining Kaio-ken with any transformation is well established. During the Tournament of Power, Goku's use of Kaio-ken times twenty with Super Saiyan Blue left him temporarily incapacitated. Stacking it with SS4, a form that already places significant demands on the body, would logically compound those risks. In Heroes, the form is treated as a last resort precisely because of this danger. The user gains a massive power spike but can only maintain it briefly before the physical toll becomes unsustainable.