How does Goku activate his Kaio-ken in Super Smash Flash 2

While playing Goku, hold down Down+Special, so Goku yells, "Just getting started!" Blue sparks should fly out of Goku until they touch an enemy, so Goku can accomplish the Kaio-ken form. As long as Goku is in Kaio-ken, his damage % constantly increases until you do Down+Special again to transform back into regular Goku, die, or wait too long before you hit someone, since Kaio-ken Goku automatically reverts back to normal if he doesn't continue to hit someone.

Therefore, Kaio-ken Goku can't charge his Kamehameha much, so you should focus on using his physical attacks, which gain more power and knockback. The most significant change in Kaio-ken form is Goku's Side-Special Kaio-ken Attack, which unleashes a series of hits to devastate the foe if the foe gets caught in this combo.